May be there are some sort of server problem on the page due to huge traffic.please retry  after some time have some patience,problem will be resolved soon

Feel free to ask me in the comment box if you are having any further doubts

hope you find it helpful 

Good Luck!

Dear Vaibhavi

If a candidate has already registered and made payment in round-1 and had not allotted a seat or opted for free exit, then no need to do it again (may be thats is why its been showing already registered)but have to make fresh choices again for round-2 by using the same login credential as used in round-1 . .

However, If a candidate is registering for the first time, then have to newly register and make payments.

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 this helps you.