So I had a Taco Bell burrito for lunch and I know it's not healthy?

We've been traveling a lot lately, so we've been eating out, too...pizza, burritos, nachos, etc. We just got back last weekend and we're going to traveling again soon, probably in a couple of weeks. I've been trying to eat healthy ever since we got back but my dad bought me and my brother a couple of burritos for lunch without telling us, so it kind of messed up my plan. I'm afraid that the burrito is going to make me gain all sorts of weight. I'm a teen who is supposed to be gaining weight for medical reasons, but I want to do it healthily. I know I should be getting as many calories as I can get, but I don't know if I really want them from junk, you know? How can I stop feeling so guilty and unhealthy?