If you feel uncomfortable with the offer, withdraw it and make the lower offer with the other agent. You're not in any binding agreement or contract.
Having been through the process in Galway in the last 6 months, I can verify that estate agents are not above sharp practice.
For example house on the market at a figure for 5 weeks with no offers, asked the agent the story. One employee tells me the vendor has bought (with the same agent at auction), so absolutely needs to sell in next 4 weeks. We put in an offer approx 10% below that, and immediately there magically appears another bidder who offers slightly more. After a increase of a few K, I told the agent we were going no higher, so to consider us out of the bidding process. After a few more pressurising phone calls from the agent he finally gives up.
Lo and behold a week later, agent rings back asking us if we want to increase our offer again. Told him my position hadn't changed since the previous week, and asked where the other mystery bidder who had offered more had gone to.
One week later the property was taken off the market.
The lesson as far as I was concerned is offer what you can afford and think it's worth, and try to avoid playing into the auctioneers hands by getting into a bidding frenzy.
I also found in Galway that going above the stamp duty limit for first time buyers, if you can at all, even with the pain of the 10K cost, was worth it for location.
Alot of houses over 317K seem to stick, and there tends not to be as many chasing them.