Felpro Oil pan rubber seal seems too big

I used a one-piece gasket in mine but remember that the seal that came in the rebuild kit didn't fit all that well on my 360 either. Actually neither the one-piece or the piece that came out of the kit fit as good as I would've liked. I'd say The Right Stuff(tm) is your ticket here, at least it was for me.

FWIW, it was expensive but it isn't leaking. Mopar Oil Pan Gasket