Are two ties enough to get my dog pregnant?

i have recently bred my kc reg shih tzu with another kc reg shih tzu. they successfully tied twice on the same day within hrs of the first tie. the stud breeder said that mine will definatley be pregnant as result but ijus want a second opinion. the male dog i used has produced healthy litters and mine has had 1 litter 2 seasons ago so both are fertile, thanks i am looking for genuine answers only please an not a load of abuse thanks