You can set the eth.defaultAccount For which you want the contract to be executed.
Your expectedSender is still not visible to useus. So, We don't know what is that, but in most cases if it is used as the owner of the contract, then it is the account which published it. Check what account published it. You can see the transaction log from your console.
You can check the number of accounts you have by
personal.listAccounts;
And see which of the address matches from the transaction log