8 days late, negative pregnancy test?

So today is day 8 of my missed period, so I took a test (first response), and it came back negative. 
Long story short I started my pill last wednesday(the day I was supposed to start) and took 2 a day until I was caught up (as recommended by my dr). I wasn't on birth control last month, due to new year insurance problems. I had sex twice, but he never finished in me.
How likely is it to be a false negative? Could I be pregnant?