According to the eligibility criteria, for a Candidate to appear for M.Sc Mathematics for IIT JAM, he/she should have completed Bachelor's degree with Mathematics as a subject atleast for 2 years or 4 semesters. But if you have studied only 3 Semesters, unfortunately, you might not be qualified for IIT JAM. Please read our article for more information: https://university.careers360.com/articles/jam-eligibility-criteria