How Do I Get My Friends Back?

I have recently fell out with my 4 bff's and don't know why they fell out with me. When i try to talk to them they ignore me and i want to know the answer so i can fix it. I tried leaving them alone i tried pestering them i've tried everything . The worst part of it is im going to my other friend's sleepover this friday and they will be going and last time i was around them they just ignored me and made me feel really bad. I dont want to to ruin my other friends birthday but i feel if i don't go she'll no want to be my friend any more and i dont want that either. Basically i just want to know how to get my friends back.