Jlags,
Don't take this the wrong way, but you both need to get a wiggle on here and get organised. The Finace(e) visa is valid for 6 months and unless you have good reason and request an extension in good time you need to get married and apply for FLR.
There shouldn't be any problems fixing up a registry office wedding and going through with it. Just a few witnesses required and that's it.
Worst case scenario is a last minute long drive up to Gretna Green![]()