Can I get into Heritage Institute of Technology with 22,000 GMR or will I have to opt for donations?

This might sound weird but there are better colleges available with your rank. Most importantly, Heritage Institute of Technology won't admit you to any of the branches with 22,000 GMR. Hop onto the next best option because there's much more to life than a college.

Another great option would be Techno India, Salt Lake. It is a wonderful college, amazing with placements, and has an ultra-modern infrastructure. The location is advantageous as well when compared to HITs. Also, you'll get the Mechanical or the Civil Department there.

Regarding donations, I do not think there is such a process, nor would I support it if I knew. Work on your scores, get selected based on merit as it will be more helpful throughout your life. 

Any college will be great if you are hard-working, so in the end, it boils down to you, college is what you make of it.