Congrats on getting good marks in 12th. So, as you told you gave JEE this year but your rank is not so good for admission in IIT or NIT and you want to become an IAS officer. According to me, you should take admission in graduation in whichever field you want either it is engineering or b.sc from any good university like DU and other many options are available instead of dropping one year. Civil services wants only degree as eligibility. It's not necessary that degree should be from IIT or NIt. So take admission and start preparing for civil services.
Good luck for your future and best wishes
Since you are very clear about your ambition (that is to become an ias officer),so galing a drop does not sound good.if you are up for btech then wait for reap result.otherwise since you have scored pretty well in your 12th ,so you can also pursue graduation in any subject of your choice from delhi university.
Make sure that you start peeparing for civil services examination from the very begining because it would not be so easy.
You might have some different views.
Its upto you.
Hope this helps,
IIT/JEE 2020 Online Preparation
Crack JEE 2020 with JEE Knockout Program, If you Do Not Quality- Get 100% MONEY BACK