20yo freelancer, earned ~20L this year, never paid tax — completely lost, need help

Hey everyone,

So I'm 20, I'm a freelacner, started earning properly from March 2025. All payments from international clients.

Total income this year is somewhere around 18L-22L (hard to pin exactly because of how payments come in). I have not paid a single rupee in tax yet — not because I was trying to avoid it, I genuinely didn't know I was supposed to pay during the year itself. Just found out about advance tax like last week.

FY ends in 33 days and I'm a bit stressed.

Few things I want to understand:

1. How much trouble am I actually in for missing advance tax deadlines?
2. Is the interest penalty going to be massive or manageable?
3. What expenses can I deduct as a freelancer?
4. Should I file under 44ADA presumptive scheme or regular ITR-3/ITR-4?
5. Is there still time to do something before March 31?

I'm going to get a CA but just want to understand the basics before I walk in so I don't get taken for a ride.

Any help appreciated. Be brutal if needed, I can handle it.