I get 72 percent in my board but i am in top20 percentile of my board i have drop for iit jee this year and give in 2020 this top20 percent

To qualify for jee advanced , you either have to be in top 20 percentile of your board category wise  or score 75 percent (for general and obc) and 65percent for other categories.

If you are in top 20percentile then for the next year, this top 20 percentile will be considered, so you can surely give jee with this percentile.

Hope it helps.