Like others have said, $100 is a lot. That’s the kind of gift one might expect from a direct family member. $50 would be plenty.
Flowers and chocolate on top of that will come off as trying too hard and showing romantic interest. Spare yourself the accusations and tension it will cause between you and your friend. It’s a very easy target that people this age will make fun of you for, even if you just intended to be polite.
Nirvana’s version of The Man Who Sold the World.