Welp, it's done! I'm not sure what was wrong with it but I disassembled, reassembled and magically everything worked. Everything fits, although I think I need to redo the cable management in the back as the side panel over there fits very snugly. I have a few plans in the future, such as replacing the PSU with an SFX one, custom-length cables, and then seeing if I can swing a small monitor in there for temps and things. We'll see.