Put both pads back into the caliper. Use a large channel lock pliers and grip on side the brake pad and the other the outside of the caliper. Try compressing several different times.
Also, with all the pads in the caliper, try alternating between stepping on the brake pedal and compressing as per above.
The reason I don't like using the C-clamp is it can too easily make the piston twist slightly going into the caliper.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)