decoupaging difficulties...

[missluwanda.livejournal.com]

hello all!
i'm made a collage out of photos from magazines for my friend's birthday and glued them all down on a piece of construction paper. my only problem is that when i decoupaged over the whole thing, the edges of the construction paper curled. any ideas on what i can to to make them not curl? i'd frame it, but that would cost way too much for my poor self to ship. all and any help is muchly appreciated!