My prom date avoids me?

well i asked this girl that I dont really know that well to jr. prom and she said yes. I kinda did it without really thinkin cuz i really needed a date after my friend couldnt go. I figured everything would work out ok and I would just start talkin to her but it hasnt worked out. She like started avoidin my eye during cl, and avoidin me in general. Everytime I like hang back after cl she starts walkin even slower and talking more intensely with her friends. One day we were in the comp lab and i saved her a seat but she made up some bull about tellin her friends she would sit with them. I really wanna get to know her a little better b4 prom but I cant bring myself to talk to her when she is with her friends (which is always). It doesnt help at all that she is like avoiding me. What should I do?