I would like to suugest you that if you are going to coching then they will surely alluring you to take their material or test & Guaranted you that you will get in to IITs or NITs..but you know the truth..

My suggestion is to prepare by your self..Take material & notes from your any friend who took coching from last 1 year..Go through That notes..Try to giving mocks(Daily).Refer all the concepts whichever u knew already..Don't go for new topic which u can't cover in 1 month..Try to giving sctional test..Solve as much as old JEE advance papers in brief..U can crack exam with good percentile..Don't lose hope & stay comfident till the real day..

Thank you