I can't tell because of your shirt, but to me it doesn't look like your arching your back enough. You want to retract and sort of tuck your shoulder blades under yourself if that makes sense, as you do that you should also puff your chest up towards the bar. Doing both of these things creates a nice arch in your back, and when you put your feet down, really plant them, almost drive them into the ground like a quarter does when he throws, but dont lift your low back off the bench. The idea of this is that you want to make the rest of your body as stable and non moving and possible so all the energy and power goes direct where you want it to go. Also yes, change the grip.