Self-conscious in my prom dress... fat arms!?

My prom dress is gorgeous, and it really makes my body look skinny. It flatters my curvy figure. The only thing is, my arms look SO fat. I never wear anything sleeveless because of that. I don't know that to do. How can I fix this problem? My dress is strapless and I'm not changing that. Can I lose weight to make a difference in only three weeks?