Registration

Yes you have taken registration volunteer, and having GST Number, you are liable to collect the tax and accordingly liability is to be discharged

You can collect GST on output and claim Eligible ITC on inward purchases from date mention in Certificate of GST Registration and you cannot collect gst for sale made before such date even though you file return for same but in Generally, portal is not allowed to do same

If I am not registered then can I claim itc or I have to bear the tax burden?

You can not collect gst without GST registration

No inputs on which I paid gst

Your query is not cleared...!
Elobrate with more details with following questions

If my turnover from business is Rs.3000000
- Which FY...?

Are You deal goods only or goods and services...?

Dear raja p m sir ... he has already registered himself in gst act so he has to collect and pay tax accordingly

Yes, so sorry but i have thought that he is not registered..

But,
I read the query correctly...

So,

I'm Waiting for reply from Querist...!

Answer to your first QUESTION :

If you are Registered under GST ( no matter Compulsory or Voluntarily registered under Section 25(3) of the CGST Act 2017 ), then it is "COMPULSORY" to charge GST on your Outward SUPPLY ( i.e. Sale ) from your customers and claim ITC on your input ( subject to Section 17(5) of the CGST Act 2017 i.e. BLOCKED CREDIT ).

For charging GST, we do not see the Turnover limit. Even if your Aggregate Turnover is Rs. 1 lakhs, you have to collect GST from your customers and deposit it to the Government and have to file all your Returns, because of the very fact that you are "REGISTERED".

Q2). If I'am not registered then can I claim ITC ???

Answer : Big "NO".... Only Registered Person can claim ITC on their inputs, input services and capital goods.