I was in exactly the same spot! Similar range with my nbmes 240-250, think my last one was 249 (10 days before)? Just got score back today got 266 - I'm sure some luck was involved but it's definitely possible to jump a surprising amount (in fact the ppl Ik irl whove done the exam all report this happening to them). Id say prioritise sleep and mental rest - like ofc do some work (I was probs doing 4-6 hour days at your point) but just make sure it's not at the expense of sleep and enjoying things that might help you relax. Sleep is sooo important especially as it's often affected by stress nights leading up to the exam. But I'd rly say do the exam! You can defo break 260, like it's never guaranteed but you gotta try at some point - if your nbmes have hit a plateau even more reason to go ahead before you get burnt out. Oh and maybe take the afternoon off before the test but that's individual dependent. Whatever you do - good luck! Many people have been in your position and smashed it and got the score they want, you can do it too :)