Soo.. there's this girl. A whiiile ago on facebook, she messaged me "i really miss you can we please hang out soon".
I told her we would chill soon.
Like the funking idiot I am, I made a promise and didn't keep it. My excuse to why that happened is, I'm struggling to graduate from highschool (I'm 20) and I didn't have any balance in my life during highschool (going out with friends, partying). Now the opposite has happened

I don't see my friends or have fun. (I used to blame my parents that they didn't want me to have fun, but I've finally accepted that it' my own fault and they are just looking out for me, they never ever didn't want me to not have fun, just wanted me to pass HS and move on with life).
Flashfoward to 2 weeks ago, I sent her a happy 4/20 text ( Don't judge me! >.<)
She replies "Happy pot head idiot day, I miss u"
We texted back an forth a bit about life and whatnot. Then I asked her what she was doing today (4/21). She said she was working and that she will text me soon. She didn't. I'm assuming it was because what I did, I don't hold anything against her, who wouldn't be mad when someone doesn't hold a promise to them..
I don't know what to do. I've made progress on my course work and am feeling like I deserve to have some fun and chillout.. I want to hang out with her but I don't know if she wants to hang out with me anymore. I asked my older sister what to do and she said just give her some time and when you have some school work done you should kick it. Well, I've done a good amount of work, preparing to write my second module test. After I write it, I want to hang out with her. I don't know if it's been long enough though, I don't want to upset her more. After my test should I try texting her?
Any insight would be appreciated, thanks.