Try this as a warm up for sprint sessions. I’d ditch the jog you’re doing as it’s not really necessary. Keep your speed sessions about speed.
Good that you’ve got the awareness of your lower back arching. I’d develop your speed over shorter distances first, where you can maintain good mechanics with the thigh coming through fast rather than leaving your leg dangling behind with some horrible but flick going on. Over time add speed endurance work and work on maintaining that shape.
Sprinting is a skill that requires practice.