Tax help needed

Hey everyone! I've been working as an "independent software contractor" with an American agency for the last 3 years. I earn anywhere between 1 to 2L a month depending on the number of hours I put in. I also have really small state government job. The salary I get from the state government job doesn't fall under any tax slabs and this software side hustle(kinda main) has always been a hidden secret because we're not supposed to do any other work while working for the government. So I never paid income tax on that money. Now I kinda started to feel guilty and want to start paying my dues in the best way possible. Can anyone please guide me how to go about it and give me an estimate of how much I'll be paying?