My initial question is this: when you say that the REALTORÂ® said that she wasn't sure if your offer was enough, are you referring to the agent with the sign in the yard, or are you speaking about your agent?
If you do not have an agent working exclusively for you, I encourage you to find someone you trust who can help guide you through the process. The agent with the sign in the yard has the obligation to work exclusively in the interest of the Seller. That agent has no fiduciary duty to you, and anything you tell them may be told to the Seller and used to negotiate against you.
In this specific instance - not knowing the nature of the house you're referring to - it may very well be that there's a bank involvement or some other investor which would, in fact, respond with something like, "your ofer isn't high enough for us to consider." Even a provate party seller has that right. They might simply say, "Thanks but no thanks. Your offer isn't high enough for us to even consider a counter offer."
Good luck in your search!
Principal Broker, REALTORÂ®
MacDuff Realty Group