Hello,
12th equivalent certificate means the certificate which is equivalent to class 12 which are HSC, Diploma etc.Those who are appearing in class 12 in 2020 must upload admit card only as you will get marksheet after the results.There is still time to apply for JEE main April session.The last date is March 6th 2020 to fill the online application and March 7th 2020 is the last date to make payment.Wait until you get your admit card.If it is too late to get admit card request your college management to give it as early as possible so that you can apply before last date.