VERY IMP PLS HELPPP

I passed all subjects last year and I filled form of improvement for three subjects this year to get better marks qualify on the 75% criteria for JEE but I am out of this city I had tickets but this Indigo cancelled and now I can't give my physics exam of improvement but I have chemistry and maths still left and I can cover in that but is the something like if I don't give one exam I won't be allowed to give others or this wont be valid I really want to know because I can reach my centre only on 21st even if I try hard I want to know if I can still give maths and chemistry and is it valid or not