A single rose, wrapped in its original cheap plastic like you'd get at the grocery store is tacky. If you must give a rose, have the florist re-wrap it with some new greenery and a pretty bow. Make sure the base of the rose is firm (instead of squishy) or it will be dead in 24 hours. Forget the chocolates. It's overkill if a girl doesn't already like you.
I think you should hand-deliver it, and tell her you'd like to take her for coffee sometime.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?