ITC not in 2b

As per the GST law, input tax credit (ITC) can be claimed only on the basis of the details furnished by the suppliers in their GSTR-1 and the same should reflect in the GSTR-2B of the recipient.

GSTR-2A is a read-only document that auto-populates based on the information filed by the supplier in GSTR-1 on the other hand, is a dynamic statement that reflects the final and reconciled input tax credit of the recipient for a given tax period.

However, in cases where the supplier has filed GSTR-1 after the due date, the details of such invoices may not reflect in the recipient's GSTR-2B for the relevant tax period, but may be available in GSTR-2A. In such a situation, the recipient can claim ITC on the basis of GSTR-2A.

In your case, if the supplier has filed GSTR-1 after the due date and the invoices are reflecting in GSTR-2A but not in GSTR-2B, you can claim ITC on the basis of GSTR-2A. However, you should ensure that the supplier has actually filed the GSTR-1 and the details are correct and match with the invoices received by you.

It is advisable to reconcile the details in GSTR-2A with the actual invoices and also communicate with the supplier to ensure that they have correctly filed the GSTR-1. You should also maintain proper documentation and records to support the claim of ITC.

It's depend upon you. But claim itc as per GSTR 2B

No you cannot .
As per Section 16(2)(aa) R/w Rule 60(7) ITC is available as per the eligible ITC autopoplated on in GSTR-2B .
So you cannot claim ITC for the same in March month.

What are the consequences if i claim this ITC in march as per GSTR 2A and do not claim in the next month when it reflects in gstr 2b of next month..
do i have to pay any interest or penalty?

You have to impose Interest.

Only interest is ok. But is there a chance of getting notice for excess claimed amount,interest and hefty penalties for March period before April returns

Yes correct its officer  discretion power ask you deposit the same with interest.  

But  as per law only interest leviable

Please tell me the reintroduce date of RCM, & Rcm applicable on payment of salary to individual and rcm can pay after filling 9c (as my last 2 year rcm not paid)