Sir please tell me how can I confirm that which merchant navy institute is fake or real ? Can I make career in this field after B.sc(maths)

You may check whether institute is Directorate General Shipping approved or not at following link: http://www.dgshipping.gov.in/Content/PageUrl.aspx?page_name=ListofallapprovedTrainingInstitutes . You can make a career in field of Marine Science with B.Sc Maths.