3M 77 is fantastic stuff, but there is also 90 and 98 spray adhesive.
I think for this application, you should have used 98 (metal to vinyl). Also keep in mind there are 2 ways of applying it. One way you spray both pieces, let them dry and then adhere them together with pressure. The other way to is spray only one piece and adhere them while they are still wet. One way is instant and permanent and the other is not. (but read the instructions for more info since it has been years since the last time I used it frequently). Scuffing up the surfaces to increase surface area is also a good idea. A thicker coat is NOT usually beneficial.
And to be clear, contact adhesive and spray adhesive are essentially the same thing, just one is applied with a brush (and is much more difficult to get even), and the other is sprayed from a can.
https://multimedia.3m.com/mws/media/1084398O/3mtm-spray-adhesive-selection-guide.pdf