To answer your first question, no. There is no law that the Listing Agent has to present the Offer to Buy before the contract acceptance deadline. The Contract Acceptance Deadline is a protection for the Buyer, as they do not have to honor any acceptance of their offer if that acceptance comes after the deadline.
Now, the Listing Agent does have to present all offers, period. If another offer came in that was better than yours (which does not always mean a higher price) then the Seller has the option to accept or reject either offer.
Please remember, you do not have a contract with the Sellers until your Offer is accepted or a Counterproposal is accepted by you, so you have no legal Contract with the Sellers at this time. The "extension" of the Contract Acceptance Deadline may have been just that, time for the Listing Agent to procure other offers, so that she could get the best possible price and terms for her client, which is what she was hired for.
Best of luck to you. I would consider getting a Buyer's Agent to help you with your home search and move on from this one. There's nothing you can do here, unless this first contract fails.