Oil pan gasket seating

I finally started putting the gasket set on this Slant 6 225 motor I have in my garage that I am redoing. The problem I am having is the rear rubber seal that attaches to the oil pan and goe between the pan and block is not fitting right. One side seems to want to sqeeze out of theback end. This is hard to keep in line. Are there any tricks anyone knows of? I think I made a mess of the gaskets. I used this stuff called Ultimate black sealant the guy sold me at autozone. That stuff is messy and doesn't come off if you get it on your skin!!!