Hey, you're up "North" so, yes you could probably use another layer of flannel in the middle! How much denim have you pre-cut? Maybe you can use the smaller pieces on a different project, or a matching pillow cover? I'd really recommend getting the spring-assisted scissors (for example the fiskars:
https://www.amazon.com/Fiskars-Softo.../dp/B00083QPVW) it is a LOT of effort cutting up denim to fray the edges!