When I create my sheet sets, where there is a curve in my alignment, there is a black space outside of the matchline. When I move the matchline closer to the end of the view frame, the black space gets smaller. Then I cannot acheive my overlap.
I'm not sure what you're question is, but it sounds like you're having trouble with matchline masks. C3D uses masks to hide the mapping beyond the matchline. The masks should be set up to print white, which depends on the color table you are printing with.
Right click on the match line and select "Edit Match Line Style". On the Display tab, you can control how the mask looks.
I recommend changing the color of the Match line mask to one that is set up in your color table with Screening = 0. That will block everything behind it, but look like empty white space on the page.