
It sounds like you were too early and the slip was just the dog trying his luck. You need to try her each day until she is receptive and mated on several occasions (I like alternate days until the bitch/dog indicates she is no longer receptive.
One of my girls is not ready until days 18 to 22, and others around 15 from first colour on a tissue test.
Based on her lack of receptivity and only a slip mating she is unlikely to get pregnant.