Suggestion on employer retaining original certificates

I joined a college as an assistant professor and signed an agreement on a normal printed paper (not a legal bond) that states I must pay an amount equal to two months' salary if I leave before completing a one-year tenure. The college has also retained my original certificates. I feel that paying two months' salary is excessively high and unfair. Is the agreement legally enforceable since it’s not on a legal bond paper? What steps can I take to get my original certificates back without paying t