First double check and make sure the tab on the back side of the moldings are not bent and are in good straight condition. Lube up the groove with WD40, start at the drivers side verticle molding at bottom corner and slide molding up and apply pressure at the same time and slide into place. Then use the same technique for the lower molding starting from pass side, then slide pass verticle piece into place, then apply same technique to the remaining (2) upper moldings. Just remember to keep is well lubed.
It is always best to put the moldings on the gasket before installing the windshield, but it can be installed after windshield is in place it's just a little harder and messy.