Roden kits can be very, very 'fiddly" to build. Fit is especially sensitive to sprue nubs that stick up, and even the smallest interference from cutting and sanding. Plus, they tend to have lots of small parts in a tiny space.
You might see if you can leave out smaller, unseen or hard to see parts, to provide more clearance.
Also, see if you can find somebody on Youtube, who has built that kit, and see if they had the same issues. Sadly, sometimes, it is not you, it is the kit. If you have to, fettle the parts down to get a fit.
I've built some Roden 1/72 WW1 fighters (the Junkers "J" series) and the fit fought me the whole way. Other builders did not have the problems I had, so I guess I may just be 'Ham-Fisted' in my building techniques.
Sorry, I could not be more help.