Jan is right. The fact that someone else can put in a backup offer should not affect your signed offer. Any offer that comes in 'must' be presented to the seller by the listing agent. Nothing will happen in most cases unless you decide to step aside due to one of the many buyer contingencies in the contract. Contratulations on finding a home you like in this market. There is a lot of competition these days. One other thing, trust your Buyer's Agent,, I am sure he won't give you bad advice. All the best.
Your Castle Real Estate