As dicksoucy said, don't put any type of glue on this. CA will just leave you with a white hazy mess on the monokote if you try to use it. The best way to tack it back down is to use a heat iron, but you said you didn't have one. You can use a regular clothes iron to tack the corner down, but be very carefull you don't get it too hot. Best way would be to start at lower temperature settings and then slowly increase until you get it tacked down.

Hope this helps.