Watch this "Clearly the Best" video on how to stamp kiss.
What Kristine shows you will result in a second generation look for the image that was on the kissing stamp. What isn't that clear from the video, is the back of the stamp she used to add the green ink, is any stamp that is large enough for the paper (Monica mentions it).
One other thing about the video. You don't have to push down as hard as Kristine does onto the paper. She's got the foam insert under the paper which will help with stamping. She's on a solid surface that won't bow (if you have problems with unfinished stamped images, it may be you're stamping in the middle of a large table and the table is sagging a little -- move to an end and see if that helps).