How come I weight alot more than i look?

Well i weigh around 150 pounds and my mom is really good at guessing peoples weight and she guessed that i looked no more than 130! .. :S I dunno if its the fact that im a figure skater and have a lot of muscle and stuff. I really dont look that big i mean im kinda tall (5'6 or 5'7) I have a pretty flat stomache and i dont look huge. :S Hmmmm, and my mom things if i actually was 130 pounds id look gross.