Two things could have happened: 1. You did not give the dough enough time to relax and chill after mixing it. I recommend chilling the dough for at least 1 hour after it is mixed and before your roll it out. And/Or 2. The butter wasn't cold enough before the pie dough went into the oven. I recommend freezing the pie dough for at least 10 minutes after you have formed it into the pie dish.