Once the contact paper is covered with tissue pieces as shown below, cut another piece of contact paper about the same size and place it on top STICKY SIDE DOWN. You are basically making a tissue paper sandwich. Smooth out any wrinkles in the contact paper and make sure the two sides are sticking together securely.
Cut the "sandwich" into a heart shape and tape it in your window. So pretty! (Tip: I just folded my contact paper sandwich in half and cut half a heart on the fold. This resulted in a symmetrical heart shape. If your child is able, you could draw a heart shape with a marker and have them cut it out.)