we didn't really had proms on my first school, it was called a prom but nobody took it seriously and just weared what they felt like.
I had a tie and it was it and most people just came in very casual clothing.
---
I refused pretty much my second prom (cause I felt mentall ill that day, and couldnt really stand the social presure around me)
the third prom was great, I was dressing up with a shirt and tie and me and my partner + the people around us had a fun time.
and the forth.. well I am not really invited, cause I am a guy, and the guy who is there is a guy =(..
-
I only weared formal clothing 2 times I remember, I had a suit on when I was a kid, but its long ago and I dont remember it,
when I was to the prom I had very light formal clothes on, and once I was in london I wore my brothers suit for a musical night.
I almost never got comments about it, exept the time in london where some guy pointed out it where strange I wore a male suit bla bla bla.. and I have never wore a dress for formal.
---
so I think you should go with what you feel like, its not like your mtf, so most people probably wouldn't mind that your wear is boyish, and if they do, then s*** those.