Maxima calipers cannot be pushed in this way. See the diamond shape cut into the piston? Use needle-nose pliers and turn the piston in the housing (I go clockwise) and push on it, it will go back in. Using a c-clamp will damage the E-brake function and cause a trip to Nissan parts. There is a Nissan tool that makes this much easier but pliers work OK too, just press pretty hard as you're turning.
:loosen the brake line on that caliper a little and then compress, this may cause a little fluid to seep out.