I suggest you postpone the test. $50 bucks is nothing in the long run if it determines whether you end up in a specialty you hate or one you love. Of course making a decision based on advice from internet strangers who are really your "competitors" is a losing strategy.
I don't know you, and I don't know what you're capable of, or your circumstances, but if you have grades you need to make up for, you have to ask yourself how much of the material did you know in the first place? Plus if your cumulative uworld score after 1000q is 58%, I also think you need to pare back some of your expectations of a 240/250; it's an elite score that, regardless of what you read on the internet, is not something you can pull out of hat, or they would not carry the weight they do. That being said....
Don't be discouraged by a drop in a uworld q block, especially only 51qs. Were they subjects you are weak on? Questions everyone got wrong? If world is discouraging you, do nbme 6 or 7 to get a better gauge. Or do uwsa2, that one was a major ego boost (a totally unbelievable 262).
If you've only done 1000q so far, you are probably 3000 short of having a good chance @ a "99" score. While I've done 1000q in a week and it works for me b/c I learn by doing endless questions, it's definitely not for everyone, and you're definitely better off taking the time to review all the answer choices and knowing the material well than just cramming questions.
I know it seems that every forum member claims to gets these scores by doing uworld 97 times, following epic schedules, memorizing FA, 1 million questions, etc. These tactics may or may not work for you, and I personally don't believe anyone unless I see their score report because I know too many DBs who lied about their SAT(!) and MCAT scores.
