Hey Ishaan.

If you do not want to appear for IMU CET, you have other ways too for joining the merchnt navy. Many private colleges also offer Marine Courses and for the admission they conduct their own entrance exam. Other Entrance Exams are TMISAT, JEE Advanced, WBJEE, CUSAT CAT.

There are total seven institutes which offers the merchant navy courses listed below.

Marine Engineering and Research Institute, MERI Kolkata
Marine Engineering and Research Institute, MERI Mumbai
Lal Bahadur Shastri College of Advanced Maritime Studies and Research, Mumbai
T.S. Chanakya, Mumbai
National Maritime Academy, Chennai
Indian Institute of Port Management, Kolkata
Indian Maritime University - Visakhapatnam Campus
(National Ship Design and Research Center)

Hope this helps. All the best.