your gym teacher is STUPID, and should learn the difference between fat and muscle! MUSCLE WEIGHS MORE THAN FAT! She doesn't know what the hell she is talking about don't listen to her crap!!! If your fine with your body that is ALL THAT MATERS, don't listen to someone who probably isn't evan as active as you! Track is awesome and it results to a person gaining a lot of muscle. I weigh a lot more than what I look like, because I run too and have muscle!(:
You're just paranoid, a pound isn't going to kill you. You stated you were being active on the track team and stuff so you're fine. Don't worry so much :)