You are correct. You are shifting your butt back instead of up to initiate the squat. You are also probably cutting the squats off high and allowing your knees to come forward. The solution to this problem will come in a few ways. The first is that you need bigger legs. Eat. The second is that you need to get tighter. Control your descent. When you are dropping into the hole while praying that you will be able to rebound back up, things are bound to go poorly. Smooth descent and controlled ascent. Lean over a little more on the way down and then hold on to that angle on the way up. Suffer. However, you made a relatively important programming error:
Set your first ID squat at 330. Calculate your volume day from that. Go up by 2.5 to 3 pounds per week on your volume day and 5 pounds per week on intensity day. This will insure a smooth ride into PRs for several months on the TM. It will also allow you to get deeper and fix some of these form errors. If you don't set a PR on your squats for four or five weeks, don't worry. The beauty of the TM makes itself felt after about three months when you are warming up with your previous 5 RMs.