Dear Srinisha

No, you don't have to register or pay again for round-2 if you have already done them in round-1 for Online All India Quota or Deemed/Central Universities UG Counseling-2019 but have to make fresh choices again for round-2 by using the same login credential as used in round-1.

Before going for further steps, kindly read the instruction carefully given in links below
Https://medicalcounseling.nic.in/UGCounselling/Documents/SchemeUG2019.pdf

Https://medicalcounseling.nic.in/UGCounselling/Documents/FAQMCCUG2019.pdf

Hope it helps you.