A lock is a physical action on behalf of the lender - the money is literally set aside in your name. If the loan officer did that, you are locked. If he/she did not, you are not. They should send you a confirmation of some sort, but if they didnt, ask for it now.
Every lender works with renegotiations differently. They are costly to the lender, so they may not agree to do it over an eighth in rate - often the lender can only split the difference with you (you locked 4.5, now it is 4, so lender can offer 4.25) - so the small change may not be possible. In that case, your only option would be to cancel the lock, wait 30-90 days, depending on the lender, and lock again.
Discuss your options openly with your loan representative - ask about company policy, costs, and options, and then make your decision accordingly.