You can take a drop year if you are confident that you will get IIT. But if you want to have options, it will be better to join IIIT Gwalior and prepare for JEE Advanced. The curriculum isn’t too demanding, you will have ample time for preparation. Also, this way you will have a backup.
IIIT Gwalior has an excellent coding culture. If you are interested in coding and have skills, you can get good placement offers.
My brother was in a similar situation back in 2014 with a rank of 11,000 in JEE advanced and 28,000 in JEE Mains. If you belong to the general category with this score, there is no chance of being able to attend IIT counseling.
However, ensure that you are completely sure of your decision. If you want to be on the safer side, you can take admission to IIITM Gwalior. If you are interested in coding, you will surely do well here. On the other hand, you can also prepare for JEE side by side as it is easy to be a student at IIITM Gwalior without much pressure.
In case you do succeed, you will end up at a much better institute and if not, you can always fall back on IIITM Gwalior.