Too self-conscious to play the "Guess Belly Size" game at shower?

Is it silly of me to not want to play the baby shower game where every one guesses my belly size? I love my bump but I'm very insecure about my body stemming from an old eating disorder. My MIL keeps pushing the game and I don't know how to explain it to her why it upsets me. Am I over reacting? I don't know what to tell her...