I need help

All 당신 need to wear is a large 셔츠 that covers your panties. Thats it :P
....By that I mean 당신 can wear anything and it wouldn't matter much ;P Wear what feels comfortable.

it might be hard and difficult,

Here's your solution.

Just dress casually. Some jeans and a red 또는 담홍색, 핑크 shirt. Don't stress over it. If you're calm, you'll have a good time.

One thing 당신 don't wanna do is dress half naked.
Don't have 당신 boobs all out and crap.
Wear what ever is comfortable but classy, ya know.

wear a 상단, 맨 위로 hat, monocle, cane, just kidding just kidding

wear whatever 당신 feel comfortable in, don't stress over it, if 당신 wear something uncomfortable you'll be too busy trying to get comfortable that 당신 won't be able to talk to him! If 당신 want some real ideas maybe ask some other people that are going what they're wearing?