Should i repeat 8th grade?

ok so like i skipped kindergarten for no apparent reason. In 7th grade i had the worst year of my life i got all D's and C;s. this year i am like a straight C student as of now (1st quarter) but i know i am going to end up getting D's again because im already having A LOT of trouble and i just can't keep staying up every night til like 3 am doing hw..and like my parents bring me up very well, we live in a HUGE house and etc. My brother is a genius but i just dont get anything. i have sooooo manny friends in the grade below me and also my boy friend is the grade below me...but i dont want to leave all of my other friends in my grade behind. Also i play tennis and i am one of the highest ranked girls in 14's nationally, and it would be better to get one more year of practice before i start high school and go onto college. Same with academics like it would be good to have one more year of middle school before i go to h.s. where everything counts. I just don't want to go up to my mom and be like HI MOM I WANT TO FAIL AND STAY BACK! :)....yea so like should i stay back and how would i tell my mom?