Please try not to worry, although I know it's hard xx
Brown cm is most likely residual implantation bleeding or 'old blood' which is generally not something to worry about. Last week, I had bright red blood, enough to soak 2 pads and also some cramping. I was so scared and went to a+e but all was fine, so it doesn't always mean the worst. i was told to come back if I started getting clots but otherwise just to rest up till bleeding stopped.
Do get in touch with an epu in the morning though and get checked out. Hopefully they'll be able to do an early scan xx