It doesn't matter how well you crimp the edges of the turnovers, sometimes the mixture will seep out a little. There are a few things that you can do to prevent this from happening though. Use a fork to really tightly crimp the edges. Making sure the edges are well brushed with the egg wash will stop the pastry from drying out and cracking. You can also put the turnovers in the fridge for 15 minutes before they go in the oven which will help.