I skipped a couple days of birth control and now my period won't stop

Riley
So I was about to start my period but it was the day of prom and I didn't want to get my period. I was half way through the placebo week and I skipped the last couple days and just started a new pack. My period still came the next day and now it's been 11 days and it's still going. Now the blood is super dark brown. 
Please help!!
Thanks