Central Board Of Secondary Education [CBSE] — Class 12 results 2021

In class 10th i had score 96.6% and in class 11th 90% and in preboards of class 12 i have given my best. Then how school can give me just 86.6%.(specially in maths -95 in 10th about 90 in 11th i have not done any single mistake in preboards even then cbse has given me only 75 marks(55 marks in theory) which is totally meaningless and i feel school or cbse has done mistakes in my result. Please help me