What a sweet valentine. The Hearts Collection Framelits make this easy. Fold the red layer first and leave a bit of the fold inside the Framelit to leave the 2 pieces attached. I saw a tip to lay Press and Seal plastic wrap over any line. Lay out your letters upside down on the line. Then you can turn the plastic wrap over and place the letters exactly where you want them.
Click for supply list and printable directions.