accidental breeding after first mating

Question
I have a beautiful one and half year Labrador. For her second heat, we find a nice stud. They finally mate and had two coital tie. After a day, a street dog could enter our garden for some minutes, I just came when they were in coital tie together. The frighten dog run away, but not my worries about getting a accidental breeding.
what is the risk? What about the litter? thank you very much

Answer
If they were "tied" together back to back or side to side, then he had to have ejaculated sperm into her.  You will have a multiple father litter..You wont be able to register this litter because you wont know who the father of the puppies is.  You will have to let the stud owner know and hope he will give you a remating next time.  I guess you have learned never to leave a bitch in heat alone ever again...you have lost a lot of money. sorry It happens and hopefully the stud owner will be understanding.
nancy