I need an answer in the next 10 min, FRieND PROBLEM?

Okay my freind had a bday party at the pool, that i didnt want to go to cuz shes wayy olderr andi wouldnt know anyone, and i told her i would be late, the party started at 12 and endds at 6. i left something at the pool and i went 2 go get it, and i ran into her, and said i needed to run home and get my suit and id wud comeback, and she offered me an extra suit, and i sadi no its fine, but now im running late and that was like 45 min ago, and my mom cant drvie me, and shes gonna be SO ANGRY like i betrayed her, how can i fix this!?!?! like she prob knows i didnt wanna come but now i seem plain RUDE. I LET HER DOWN ON HER BDAY...