Is there are seats fixed for MCA at IGNOU?
As per the official website, there are no specifications related to the MCA seats. So you may assume that the seats are open and not fixed.
To recheck you may visit the link below:
http://ignou.ac.in/ignou/aboutignou/school/socis/programmes/detail/174/2
I hope my answer helps. All the very best for your future endeavors!