I asked out a girl one grade below me, and now I am really regretting it?

Well, you sort of dug your grave when you chose to date her just because her friends pressured you. To be honest with you, your going to hurt her feelings no matter what, but you may be able to save the friendship if you break up with her and fast. Considering your moving on to high school, you wont maintian much of a friendship most likely anyway, but it's your choice. You need to break up with her immidiately, but do it gently. Tell her that you dont feel like you cant give her the attention and love she deserves, and as her friend, you think she deserves the best. She'll still be hurt, but at least your coming off sounding like a good guy.