Could I be pregnant?

My boyfriend and I use the withdraw method, but for some reason yesterday he was a little slower pulling out than usual. He didn't cum inside me but he did get a little cum on the entrance to my vagina while he was pulling out. Do you guys think I could be pregnant? Do you know anyone that has gotten pregnant a similar way? Yes we know about precum he has actually been tested to see if his precum contains sperm, I was there and the doctor said he didn't have sperm in his precum. He also always pees after he cums to "flush out" any extra sperm still hanging out in there. Of course I'm just one of those people that over thinks things, he's always been really good about pulling out before.