The Stray Vacancy round is conducted by the respective Deemed University/AIIMS/JIPMER branch. MCC will forward the list of registered Candidates who qualified in NEET for All India Quota seats on the basis of their ranks. There is no fresh registration for Stray Vacancy round. You are eligible for Stray Vacancy round as long as you do not fall in any of these 3 Categories.

Joined the Allotted seat in Round 2 of All India Quota/Deemed/Central Universities

Was allotted a seat in the Mop Up Round of All India Counseling

Joined a seat allotted in  the Mop Up Round of All India Counseling

But because your case falls in none of the Categories mentioned above, you are eligible to participate in Stray Vacancy round. According to https://mcc.nic.in/UGCounselling/Documents/UGSchemeFinal.pdf , those not eligible for Stray Vacancy round of Deemed Universities are:

Joined the Allotted seat in Round 2 of All India Quota/Deemed/Central Universities

Was allotted a seat in the Mop Up Round of All India Counseling

Joined a seat allotted in  the Mop Up Round of All India Counseling

Who haven't registered for Rounds 1, 2 and Mop Up Round of All India Counselling.