re: Learning to Drive my Chevalet

I’m surprised to hear that the pattern is lifting. I get that sometimes when I’m lazy and use spray adhesive but never with HHG. Did you get the pattern down while the glue was still liquid? Did you rub the pattern down with a scrub brush?
It should be a thin layer of glue and should not have time to cool. This is a place where if you weren’t sure, you could use a hot caul after the fact and eliminate the doubt.