Hi there,
You need to work out the math here: At your current state of preparation do you have essentially a 0% chance of making it through? As in, have you not been able to solve a case with at least a 4/5 rating?
If so, you may as well postpone.
If not, what % increase will result from postponing? As in, if you have a 10% shot right now (you're 70% ready), can you up it to a 50% shot with a week's prep (i.e. get to 90% ready)? If so, postpone. If not, don't.
I would highly recommend you get a coach to assess you. They can tell you whether your odds right now are high or low, and how much more work is required. It's worth the investment (if you can find an opening in their schedule on such short notice that is!)
Good luck to you.
(edited)