This is purely hypothetical for me but I have a few questions.
1) how much chivalry is appropriate on a for-real platonic meet up/"date"?
2) how about if it's platonic but I wish it wasn't?
3) and just for completeness' sake, how about if it's platonic and I like it that way but the other person wishes it wasn't?
1) in general, any behaviour which is out of character will hit you later in the face like a flaming boomerang with spikes all over it. If you are sensitive and you are empathetic to the needs of others, by all means do wear your chivalry on your sleeve.
Inconsistency in behaviour is the number one reason why people use the word creepy. Say there's an overweight girl who's on OKC with a profile pic 1) where she shows her face and then 2-3) a full body pic which shows she's heavy-set. She knows the general consensus about body weight and she is upfront about it. Her profile is cool. You think "maybe I'll give her a call".
Then you browse the profile of a girl with the cutest face ever, she has three pics of her face in each pic slot and nothing else, all taken from weird angles. She says she is positive, honest and confident, that she doesn't like cheaters and liars.
Then you either meet her or you keep chatting on OKC and she sends full pictures, and then you see she is just as overweight as the other girl. Not only that but she also hides under long shirts, everything she has on herself is coloured in black and she keeps making self-deprecating jokes about her weight. How many other things would this girl lie about? Is she really confident if she cannot accept her weight and doing nothing about it? Could this be another girl who's overweight and says she wants to be "respected" while the entire time she dated and slept with guys who told her to her face how fat she is?
2) there are two ways to get out of platonic: a sneaky way and an honest way.
Sneaky way is be her friend and
every single time she complains about her boyfriend or about some guy she wants to date, take the side of the guy. This imply you are taking their roles: the guy makes fun of her? you say she is too uptight and she needs to learn to take jokes. the guy wants her to dress as unnoticeable as possible because he has uncontrollable fits of jealousy? you tell her she should meet his expectations as he meets hers. The guy made her wait for half-hour? tell her to learn to deal with someone who has a job/active life/dedication to sports and to respect the fact that this someone made the time to meet with her.
This projects all the qualities she looks for in a guy (she is complaining about it but she keeps going for him) onto you, and it also reverts any games she is playing on you if she is using you as a crutch to comfort her in time of need and nothing else.
The honest way is simply refusing to talk about other guys at all: you tell her she knows you have feelings for her and that you are not going to play best friend because that's not what you want. You stick to what you want and you accept nothing else: you keep behaving as chivalrous as you are, you help her when she needs it (without ever making a sacrifice you'll regret later) and you listen to her when she talks about all the shit her best friend did to her the last time they took a trip together, but you never allow talk about boyfriends, hook-ups, first experiences, or anything else connected to love and relationships. Your way or the highway.
If she can't accept that you have to be consistent and stay away from her. This road has no turning back: it's all or nothing, but the pro about it is that if you are not dealing with a tease she will be as upfront as you have and she will give you a straight answer. Most times though, you'll end up with her guilt-tripping you for ruining the friendship, hiding your true feelings and trying to control her. This is because a lot of people (guys and girls) who are in weird friendships enjoy the power of an ambiguous relationship, but they can't handle the responsibilities that come with it. Which is to say that technically, when you are in platonic friendship and it fails miserably, the fault is on both parties, who both claimed to be unaware of what was really going on.
3) you dodge the bullet with "I'm in love with this girl...", "I can't get over my ex", "I don't want anything serious right now", "I'll be gone next month for work/travel, we'll talk when I'm back" (and then you "forget" about it), "we are too similar", or the old, honest, plain "I don't see you that way". If the friendship is true they'll get the hint and they will grow out of it. There's plenty of guys and girls who won't make you feel bad for a love-confession and they will be consistent with their answers, meaning they won't twist the knife and they will forget about it as if it never happened. But then you have all this passive-aggressive people who are literally waiting for you to confess so they can play "everyone loves me but there is only one
me, OMG it's so tragic". Then passive-aggressive he/she gets sad and...keeps going for the guy/girl who doesn't answer his/her calls and replies to every message with a single emoticon and a sarcastic joke. And then you have "hey guys, what do you think he/she meant when he/she said "I have no time for you right now"? Do you think he/she is angry at me? but what did I do? do you think I should give him/her space? three days you say? but I love her/him! why is he/she doing this? Am I overthinking it? He/she said he/she was busy at work, I believe him/her".
And so on and so on.
Good that you had the courage to ask her out, take that and find someone else! Eventually you will find a girl who likes you. 
Has she responded yet?