Can't get sash out

I have a PGT double hung non-tilt window. I think it's a 1/2" channel balance, but I can't get the sash out.
I've watched the video, I pop the take-out clips out, and I raise the sash as high as it will go. But I can't pop it out of its channel. It's a big window. The sash is about 50" wide by 31 1/2" high.