I think you need to lift your elbows and move the bar a little lower on your back. It looks like your knees travel a little far forward, and that might be related to the last sentence. As an aside, I wouldn't recommend a set of 5 at 155 if your working sets are 180. Maybe something like: 45x5x2, 115x5, 135x3, 155x2, 165x1; or something...
Your press should start with the elbows in front of the bar and the shoulders raised. You want the bar resting on your shoulders when you come out the rack and not just on your wrists.
I hope that helps.