You do sound like a bit of a turd, but so did I at 15 so whatever.
Anyway, it all depends on what kind of stuff your girl likes to do. I don't know shit about Indiana, but here are a few things my girl and I have done and had a lot of fun doing:
-Going to the batting cages
-Going to the arcade (this is kind of a nostalgic thing for us and we have only gone twice, but it was just some goofy fun)
-Rent a boat and go out on a lake and have a picnic
-Make a bunch of funky shaped cookies and then decorate them (kinda like seeing shapes in the clouds but you get to draw on them with frosting to show how you see them)
-Go to a baseball game (sometimes grocery stores or radio stations sell cheap ass tickets)
-Go to a water park (it is summer afterall)
-Rent a few scary movies and spend an evening on the couch with her gripping onto you (my girl gets scared easily and it's cute haha)
-Going to do go-karts at one of the real go-kart speedways (this can be a little pricey but it's a blast)
-Go out for ice cream in the evening and just find a nice local park to hang out and talk/play on the swings
Some of these require a bit of money and a lot of the stuff my girl and I have done is pretty much impossible for you to pull off without a car and/or state bordering an ocean, but maybe some of these ideas will trigger other ideas. I haven't been 15 in a long time so I can't remember the kind of stuff I was doing... but just be thoughtful and ideas will come to you. One of the best dates I ever took my girlfriend on was when we went down to Mission Bay (San Diego) at night and went on a kayaking tour with a small group of people through the bay and then got to watch the fireworks launch over the water at Sea World. I will never forget that night. It was random as
, but it was a blast.