You most likely have a very flat turn. You need to feel that when you initiate your left shoulder turn that you start with the left shoulder starting down towards your left foot before rotating. You want a 90 degree shoulder turn to your spine angle established at address. Also try to keep your weight more on your left foot even all the way to the top of the swing. At your address position, think of your left leg and left shoulder being against a wall and when you turn in your backswing, you want to keep your left hip, leg and shoulder still against hat wall and not shift away from it. Just a couple of pointers that will surely steepen your shoulder turn while keeping your hands on or inside your right shoulder at the top of the swing.