In that case, you must select OBC NCL as your category, as BC itself includes all classes that are backward. Perhaps after confirming from the NTA as well as the Nodal Authority in your State, checking the Central OBC list. For more information do follow the link below

https://engineering.careers360.com/articles/jee-main-reservation-criteria/amp

If you belong to OBC Category, the Category you belong to should be also listed in the Central OBC list. Or else you will be considered as General Category. You can check that at: http://www.ncbc.nic.in/user_panel/centralliststateview.aspx . Go to this page and click on your State. Search for the Community you belong to. If it is there, then you will be considered under OBC Category or else you have to fill in the application form under General Category and then the aggregate requirements change. To qualify for JEE Mains, there is no minimum aggregate criteria. But if you want to join NITs, IIITs or CFTIs then you should score a minimum aggregate of 75% only in your 12th. 11th marks aren't considered. And then to appear for JEE Advanced which is the gateway for admission to IITs, you will need to fulfill the 75% aggregate condition. Now it is 75% for General Category and 65% for Reserved Categories. So how much you score in 12th is what matters to secure your eligibility for NITs, IIITs, CFTIs and JEE Advanced.