What next after composition scheme

I have applied for Composition Scheme on 25th March 2018. 

So now what returns I need to upload for changing from regular tax payer to composition? I have seen somewhere that CMP-03 need to be file within 90 days and somewhere I have seen that ITC-03 need to be file within 30 days.

So please guide me what returns need to be filed and within which period ?

Thank You.