Will Agent Hold Up Offer?

Depending on state law, which varies greatly these days, the listing agent is probably legally bound to put the seller's interests first.  That may include holding your offer until its expiration date (I hope it contained an expiration date?) to see if something better can be found.  But the agent is also legally required to present all written offers promptly, so the seller knows about it.  The seller is not, however, required by law to answer immediately--or indeed to answer at all.  That's why you want an expiration date after which you wouldn't be bound by your offer if it hadn't been accepted.