Rat Terrier Pregnant?

Question
We have a 4 yr old rat terrier male and we just acquired a female who went into heat within 2 days of getting her.  We have kept them apart for two weeks and last night they chewed through a gate to get together.  We were out of the house for 3 hours and came back to both dogs on one side of the gate and no longer interested in eachother.  Since then, the female has stopped bleeding and they don't want eachother anymore.  Is this a sign that our female is pregnant?  Can they mate without pregnancy?  Please advise.
Thanks

Answer
Michelle,   the most fertile time during the  heat cycle is the 13th.  However, just like humans She could be fertile a few days before or a few days after the 13th day.  I have heard of a beagle getting bred on the 21st day.  So it oculd go either way....Since you dont want a litter right now,,,she probably is (Murphy's Law).  If you were going to get her spayed,  now is the time.
Nancy