The first thing I will mention is about the annoying glitch you were trying to solve but I believe if you freeze the rotation of the rigid body on your player it may stop the glitch that happens when you run into the wall. Also, your panels are smaller than the screen, something I do to easily fix this is to change the scale of the panels to 1.1 so that they go past the canvas to ensure there are no weird outlines. The tracking bullets were also quite annoying especially when some of the pickups were very close to the turrets. I think these turrets would have been a lot better for the game without the tracking.