duster rear window rubber wavy inside

Hello people of the internet,newbie here with a small problem...All started when I washed the car (recently purchased a 70 duster 340), noticed water in the trunk.I traced the leak to a 47 yr old window gasket(can you say dry), so got the ol classic industries cat. ordered a gasket , locking strip and some acoustic sealer(butyl)... Then came the fight(rope guwey fingers gasket on widow/car arguments wrong helper)ended up putting gasket on car with butyl and got the window in with a rope , lots a soap , lots of love and the right helper(Thanks Kev.).Now the part of the gasket that mimics a moulding tween glass and headliner is all wavy and its ugly! I don t think I messed up installing it(ex:When I got the gasket all rolled up in the bag I put it on the car and noticed the waves but figured glass and locking strip would stretch it into place , well it didn t).

Now every one knows I have an ugly gasket in my car , here is my question...

Has anyone ever encountered this? Is there a simple trick to <iron> this out?

I am afraid to use a heat gun and perhaps make it worse!

Any and all help / leads will be welcome...

Thanks in advance.