How do you define "too long"?
Your offer should have had an expiration date on it--48 hours, 72 hours, etc. If it did, and if that time has passed, then your offer is dead.
If your offer didn't have an expiration date on it...it should have. Withdraw your offer, and resubmit a new one with an expiration date. And consider whether you want to offer more, the same, or less than your initial offer.
You say "An agent has a lot for sale." I assume you mean an agent is representing a seller with a lot for sale. (Though you know what they say about assuming...) Did YOU have an agent representing you? Hopefully yes. If so, ask your agent to check with the other agent to find out the status of your offer.