As a legal beneficiary of the will you had a right to see both the will as well as an accounting of funds in the estate account. Actually the lawyer or notary your stepdad used to probate the will should have sent all beneficiaries a copy of the document. Get his name and address from your stepdad. Tell your stepdad you suspect the estate was not settled properly and that you want a copy of all estate banking records. If he balks or will not provide you with all the details visit a lawyer.
My take is that the lawyer will draw up a letter calling for a detailed accounting of funds received and dispersed from the estate account. If your stepdad has cheated you, your call and the letter should put the fear of the law into him as executor.