School Prom

I've said it in my bulletin earlier before but an old friend invited me to prom. But now I'm panicking on the dress or tux to wear. I have 2 fancy dresses I thrifted at a garage sale last year. I'm trying to find local businesses that can help me make adjustments if possible/needed. She also sent me a picture in her dress that looked very prom-like but said I could be casually dressed if I want 'ta. So now I'm debating if I should tone it done with fanciness and go prom dress with a little visual kei and lolita. Or go casual vampire goth lassy seeing as it was the outfit I planned to by 2 weeks prior to be asked for my own fashion sense. A normal tux or victorian tailcoat vibes if I wanna dress more masculine. Any help here? (

P.s it's my junior year I wasn't planning on going until she asked me to tag along.)