Dear Kiya,
        If you wanted to do BTech from a reputed college such as nit or IIT or various You should complete your 12th first as high school qualifications are mandatory for the entrance exam for these papers.

And if you want to join any state level engineering college you can go for a diploma for 3 years and then join the engineering college by their lateral entry program directly from 2nd year and complete your BTech in just 3 years .

It's up to you what college you choose according to my opinion you should go directly for b tech i.e, complete you high school graduation first and then complete your BTech in this way you can get a good college.
Regards