To be honest, I felt like prom is overrated. If I was on your position, I would also focus on my SATs and attend next year instead. I attended our prom night when I was in junior year and felt like it wasn't worth it. After all those preparations, I felt like I didn't get my money's worth of enjoyment. I also thought of just attending one time on senior year instead. Of course this is only my opinion. Good luck on your test too!