We are a bit limited with just the side view, but a few things: 1) keep your gaze on the floor slightly further ahead even between reps. 2) make sure your hips and knees break at the start of each rep at the same time; knees are lagging a bit. 3) bear down tighter on your abs to keep your back flat and get a belt that isn't wider in the back than it is in the front. 4) I would also pause a touch longer between reps to catch your breath and get tight. The set seems a bit rushed.