@Marsha-Kay-Ottum-Owen There are sure to be some "photo editing" or "photo manipulation" tips-and-tricks and tutorials online that can perhaps give you help on "stitching together." Though they'll be about photography, the basic process is the same as with merging 2+ illustrations: Masking, Cloning, Levels/Curves Value Manipulation, Hue/Saturation & Color Balance, Opacity & Effects, etc.
In my opinion, this would be a great "next digital skill" for you to pursue as it could give you a lot of freedom with your traditional artwork, particularly for fixes, but also it may give you some tools/tricks for any desired enhancements or simply allow you to create pieces as separate elements (for instance, if you wanted to paint the character(s) separate from the background so that in addition to the digital merging of them for piece #1, you can use the characters elsewhere as a spot illustration or with another background and if you want to use the background elsewhere too without having to repaint them)