Please help me with this situation? easyy points! :)?

Alright so one of my good friends texted me this morning and said i have to come to this pool party with her on saturday. i was alirght with it at first but then i found out all the people going are either realllyy skinny popular bitchy gorgeous girls or these asshole hotty jock guys who make fun of eveyrone. when she told me all the ppl that were invited i got really uncomfortable and decided i really dont wanna go cuz first oif all im not friends with any of them and second im a little chubby so im gonna look disgusting and proll get made fun of the whole time for wearing a bikini! we also dont really talk to any of them so its gonna be mad awkward for me, and i feel like shell leave me to hang out wiht guys she knows cuz shes a huge flirtt.the problem is i just canceled on her for something else and shes not going if i dont go so i feel terrible if i cancelled plus i feel like shes gonna find out if i make up an excuse. shes not the most understanding person either so i cant just tell her why i dont wanna go cuz she wont take that for an excuse. i reallyy dont wanna go to this but am i being unreasonable? and how cani get out of it? thank youu so much!