Well... if you have stuck with May so far, you might as well stick with her until the tournament is over. I wouldn't suggest switching to a new character 4 days before the tournament. Anyway, May isn't that bad at all. She is middle tier; has no extremely bad matchups and can accomodate a lot of different styles (rushdown, turtle, etc).
I don't play May seriously, so I can't give you any crazy tips, but I can suggest some general things.
May's 6P (f+P) = Godly. It does like 300% stun on normal hit and like 600% on counter. It's a LV4 attack, so that's alot of stun! So if you land it like 3x, it's very likely that the opponent will be dizzy. It's got good upper body invulnerability (around 18frames), so you can use it as anti-air, anti-fireball, etc. 6P, s.S, 6P is a decent combo as well for helping get that dizzy. Some people even use the dizzy to setup her instant kill since her IK transform is pretty quick. Might be an option for you if you are still close to the opponent after the dizzy.
Standing K is good too since it avoids lows at non-point blank range, can't be thrown, and starts her pressure strings.
IAD (instant air dash) H is hella good and has a huge hit box. Jump 2H is her best air to ground attack and can crossup and can be just plain annoying if you use it well
General combo.... 2K-2D -> dolphin upper > FRC, a.H, land, IAD K-H, land, dolphin upper. Thats pretty tough, but worthwhile to learn. At least learn the 2D -> dolphin upper, FRC, a.H combo. For general B&B, you can just use K-1S-1H -> dolphin across, FRC and followup with pressure attacks like falling H (after the FRC) or stuff like IAD H or j2H.
Best supers..... HCB+H for midscreen stuff. Good invincibilty on startup and decent damage. If you have your back to the corner, use the whale (QCFx2+S) super. Great invincibility and is instant with your back to the corner. Against light characters, you can standing S into air combo after it. For everyone else, I usually just followup with 6P -> dolphin hoop setup.
Use her command throw (Overhead Kiss aka. OHK). Great range, and easy to tick into. You can tick into it off of a blocked 2K or standing K, or set it up off of hoop fakes. (Like knockdown opponent and setup dolphin hoop above them (hold the button), then run up and OHK.) OHK is hella good, so mess around with some setups. If you connect it at midscreen, you can followup the throw with like j.K-H, land j.K-H->623S type stuff. Thats pretty difficult though, so you may just want to use a single j.K-H->623S followup. You can also combo to whale super versus mid/heavy weights, but that's kinda wasteful. Only use that at distances where the j.K-H followup won't connect.
Know her dolphin hoop distances. 236P = on top of May, 236K = in front of May, 236S = in front of opponent, 236H = on top of opponent. Good for pressure on wakeup. Can be FRC'd as well, but probably not necessary for you. Also, 236P is decent as early anti-air as well since the dolphin hits on the way up as well.
May gets good damage off her dust, so be sure learn her dust combos. You'll be playing the US version probably, so I don't really know what her best option is there. (Her jD is different in the JPN version, so her typical dust combo doesn't work in the US version. You're gonna have to experiment and figure out the best one.)
Only problem with May is that she lacks some solid anti-burst stuff, but I don't think you are up to that point anyway.
Like I said, I got the game in February. I've dabbled in most characters, learned most combos-- I only settled on May for a bit here because she's not conventional like the others and I really enjoy screwing with people in games. I've contemplated Zappa at times but I think that's extremely high caliber playing that I'm not ready to invest in at such a level.