I loved this sweet but sporty lace dress at Sandro.
(It took me a while but I suddenly remembered what it reminded me of. When I was about 17, I had this tracksuit made by Johan Cruyff Sports, Johan being Holland's best football player ever. One of my parents' friends ran the company and I think we got a good deal on it. The first time I wore it was at a team tennis match against a neighboring town. The other girl on my team, very pretty, stylish, and bitchy, virtually immediately announced that tracksuit was butt ugly).
I think this dress would be even better with some crazy mismatched accessories - why not add some more (but different) stripes in a roughly matching color palette.
And then some shoes with a little bit of sweetness and edge, but make sure they are flat to keep it easy and relaxed.
(I proudly kept wearing the tracksuit. For as long as I can remember I never wanted to look like everyone else and I took great pleasure in ignoring my pretty teammate's pronouncements).