Sadie hawkins??? girls please help?

Today at school I got asked Sadie hawkins dance (girls ask guys) by a girl I barely know and don't like that way. I panicked and said I couldn't go, but I really want to go with another girl named Hannah. She was gonna ask me, but if the first girl sees me it will hurt her feelings (bad because I sit next to her for several cles). What should I do?