Hey guys I think I have a problem can anyone help?

I was suppose to start my period tomorrow the 11th but I almost had sex yesterday there was penetration but we didn't have sex because I told him to wait/stop. And about an hour later I started brown spotting when I went to the restroom. I began to check frequently and then it change from just dark brown spotting to red blood and dark brown (more dark brown than red) and when I would wipe I would have dark brown clumps. This has never happened to me before. Could anyone tell me what's wrong because I've had full intercourse a day or two before my period and this has never happened.