Idk what to do

I hate my life so much, I’m 14 and I’m gonna turn 15 next week. I’m in foster care and I’m just an absolute waste of space! I can’t do anything right, I’m failing at nearly all my subjects, I keep making my foster carer’s (I’ve been with them for 8 years) upset with me. They call me a liar and it pisses me off so much . I’m fat and ugly and stupid. I feel stupid for writing this I just want to end my life! Right now. I have pills next to me as I type and I really want to take them just so I can leave this world. I’m a mistake and I’m useless. I just don’t want to leave my friends. I’m supposed to be seeing my mum this Sunday. I know she’ll get sad if I kill myself but I’m just fed up of living on this earth! I’ve tried to overdose before but I only took a small amount , so nothing even happened. I’m so stupid I can’t even kill myself properly. Like most I stumbled across this by researching  how many I have to take and etc. my foster carer’s have done a lot for me which I’m grateful for but they’re so restricting I hate it. I just don’t know how to live I don’t want to stay anymore. The only thing is, what if I fail again i’ll just be stuck here again.