Skylar,
Just eat healthy, lots of vegetables, some fresh fruit and a little lean meat or other protein source.
I now eat 50% vegetables, 25% fresh fruit and the rest is a little bit of lean meat, breads or grains and a little dairy.
You will be just fine.
Those of us who are over weight need exercise to help lose the excess fat. Under weight people need to build muscle mass, not excess fat. This means a double portion of the lean meats and strength training. When you hit the weight room, do not forget the stretching exercises. In my younger days, trying to be macho, I lifted weights. Stretching helped keep my range of motion as it should be. Other weight lifters who did not stretch soon became muscle bound, that is they could lift much more than me, but were much less athletic because their range of motion was very limited.