Valentine's day help please :)

Hi! I'm a 17 year old male and I'm going to be having my first valentine's day with a boyfriend, I've already made reservations at a nice restaurant, got nice clothes, a card and some chocolates (one has a little teddy bear on it and it's super cute -). I just don't know when to buy flowers cause I don't want any stores to run out and then I'm left there flower less :/ and I don't want to disappoint which he said would be impossible but I'm really nervous and excited, also is a white button up shirt black dress pants tie and blazer too much..? Idk any advice would be great :)!!