I work part time in the USA with a H2B working Visa. My W-2 has deductions for Fed. Income tax withheld, which I understand, but they have also deducted SS tax as well as Medicare tax. Can I not have these deductions returned to myself

No. You have work visa and must pay taxes like a U.S. citizen or resident.

If you are not a U.S. resident, no SS is due.