Suit malfunctions

About a week ago, I bought a suit for speech and debate tournaments on amazon. The size charts were WAY Fing off and the suit came in like 2 sizes too big. I’ve tried safety pins, but with my piece I have to get on the ground, and every time I’ve practiced in the suit, it pops off. What do I do?? I haven’t had time to get it tailored and I need it *TOMORROW* how do I keep the safety pins from popping? Is there a better way to make it actually fit me last minute? Please help...