Hollye's right, if you had a internal scan the blood could be from that!
But than i would always play it safe and if your concerned or it continues than i would get it checked out - my first M/C started as very tiny brown spots! and it was after we saw a heartbeat. You can never be too safe! Tho chances are all will be fine!
And as Hollye said being paranoid never stops! once your pregnant and ur a mum u worry about everything! hehehe