It is normal to see a drop in the score during the last few days. First thing to understand is that your preparation is not the problem. Calm down.The reasons behind the drop can be:
1) Poor mock test analysisIf you have no idea where you are losing marks, you’re just not analysing your tests properly.Use a good analysis strategy to understand your mistakes and deal with them.
2) Lack of RevisionYou might be feeling like you are forgetting everything. This leads to random mistakes in mock tests.Revise your weak topics after mock test analysis and go through formula sheets everyday
3) Exam anxietyEvery test you attempt comes with a lot of pressure to perform well.Take help, talk to people. Talk to your parents, you teachers or anyone else that is dependable.
4) BurnoutIt is natural to feel tired in the last few days.I want you spend some time doing whatever you like most, I would bake/ paint because it helps me feel calm.
Identify the problem and deal with it. One important point to remember is that you should not stop attempting mock tests even if you are scoring low. Consistency is important