If you need to re-pay the difference, say you earn 70K per year and 7% FICA(SS/OASDI+Medicare) was short for 6 years. That is $4.9K x 6 = almost $30K, a value exceeding a brand new V6 top-class Accord or Avalon. Can you afford to pay given that you may be laid off soon?
If I were you, I consider my self lucky for evading those. Dodged the bullit. Because I expect I can work 10 more years and still qualify Medicare free part A. And missing 6 earlier years in my career really won't lower my social security income (pension) rate when I retire.