Sewnup is a somewhat uncommon word, but if you're looking for synonyms, there are a few options to consider. One option might be "sewn together," which describes two or more pieces of material that have been stitched or otherwise joined to form a cohesive whole. "Mended" or "repaired" might also be appropriate, especially if you're describing the fixing of a tear or other damage. Alternatively, you could use "closed" or "sealed," as these words convey the sense of something being secured and made whole. Depending on the context, other possible synonyms for sewnup might include "completed," "finished," or "resolved".