I don't think you are messed up at all. What happened to you, and what happened to the one who did that to you was messed up. Behaviors like that are learned.
It's kind of hard to say if it's abuse or not. You were both underage and both willing, like you said. But pertaining what happened between you two, you were also both victims. I think it is more up to you to decide what it is, than us.
rainn.org has a free anonymous online hotline (and phone line) where you can talk to someone about it, if you are comfortable with that. Although your situation is different than mine, it's very similar. I used it and they helped by telling me that even if what happened wasn't violent, or if they didn't have cruel intentions, it could still be classified as abuse.
Since you were affected by it, I recommend their site. Someone there might be able to help you sort it out and find resources if you need.

Know that you are not messed up, or anything else negative, because of what happened. You are not alone, either. There are a lot of friendly people here who lend their ears, so don't be afraid to post if you need to take care!