TDS calculation

Hey all,

How is the TDS on income from freelancing or consulting calculated. Apart from my job, I am also a Software Development mentor in a startup. They deduct the TDS on a per session basis at 10%. Which means if the per session rate is 100 rs, they send me 90 rs.

I tried filing it under ITR 4 but my freelance income is now being considered under my regular income, and now I have a big tax to pay apart from advance TDS already paid by my employer and the 10% one where I work as a freelancer.

Ideally what should be done in this. Or is there no way to do anything. Can Anyone experienced in this guide me?