I got a lead role in my school's production of "Chicago" but I'm too fat

Soooo my school is doing a play of the Chicago Musical! I'm really excited for it because I auditioned and surprisingly got a leading role. It's for juniors and seniors only (I'm 17, so senior) My friends were really happy for me and this is my costume for the Cell block tango

My mom said I looked amazing but my dad started laughing and covering his mouth when he saw. I asked him what was so funny and he said nothing. Then I went upstairs and heard him telling my mom that I was gonna embarrass myself. Now I feel very discouraged.