Normally sellers will ad a remark on the listing that the sale is contingent of purchasing another property, in this case your realtor didn't tell you that it's ok.
You can always try to talk to the buyer because life is not only contracts and papers, the buyer might have a heart and he will understand your situation.
I got things done like this before many times for my clients. it might going to work for you, but it doesn't heart to try.

Michelle,

You should have mentioned in the MLS listing and the first counter offer that the sale would be contingent upon the Seller securing a satisfactory replacement property.
But keep in mind that given market reality it's difficult to obtain such a concession from Buyers since it empowers the Seller so and potentially leaves the Buyer hanging.

No one wants to move twice - sorry. Try making lemonade... find an even better value in a an even more attractive home - the market is still working for you.

It sounds like you didn't include the Seller Contingency to find a replacement property when you agreed to the Buyers Purcase Agreement, which means you don't have the right to cancel the contract.

If you and the Buyer did agree and both signed a Seller Contingency to find replacement property then it is likely that you can pull out

Your agent should be able to help you out in this situation.

Maybe you can offer the buyer of your property some sort of incentive to voluntary cancel the contract based on their Investigation Contingency

I'm so sorry you find yourself in this situation, BUT the good news is that there are at least a lot of properties to choose from in this market and it's much harder to find qualified buyers. So maybe you can find another replacement home that fits your needs?

Good luck to you!