Front Driver Disc stuck?

[muddpile]

Since I'm doing a full resto, I decided while I was at it, I'd replace the master cylinder. It leaked a little, and was so rusty you could hardly tell what it was. I bought one from the parts store, hung it on the firewall, hooked up the proportioning valve and brake lines, and bled the prop valve with the little screw on the front. I then bled the remaining brakes until clean new fluid came out (I basically flushed the system. Now, the problem is that the front drivers caliper is now clamped down tight, no movement. The other three brakes are fine, but that one is now stuck. Should I open the bleed screw and use a C-clamp on the piston to clean out more fluid from the caliper and see if that's the problem, or is there another thing that might be wrong? Thanks!