If you're unsure whether you're immune to measles, you should first try to find your vaccination records. If you do not have written documentation of your vaccination records, contact your Healthcare Provider to obtain your vaccination records. If you are not vaccinated against measles, you should get vaccinated with the measles-mumps-rubella (MMR) vaccine.
Another option is to have a doctor test your blood to determine whether you're immune. But this option is likely to cost more and will take two doctor's visits. There is no harm in getting another dose of MMR vaccine if you may already be immune to measles (or mumps or rubella).