Jane
Your Realtor, someone who has read the entire purchase agreement, is the one to be giving you advice.

This is not legal advice. Normally in the course of home sales it is not too uncommon to have a buyer get cold feet. The purchase contracts are written to allow the buyer numerous ways to opt out if the property is discovered not suit their needs and preferences. As long as you are still in the contingency period you are probably okay.

Ask your Realtor.

Janeshaw, do you have an agent? This would best be answered by your agent. It's hard for us to answer a question like that without knowing how far along you are in your purchase. If you cancel too far down the line, there may be legal and financial ramifications. Check with your agent. If you don't have an agent, check with an attorney. You may end up paying some sort of costs for the buyer to help them with their expenses of the delay of being able to move. And, there's a chance, depending on where you are in the process, that the buyers may have a right to sue you for specific performance. Again, I'm not an attorney, I suggest you check with the professionals you've hired first to find out how far along you are.

Janeshaw,

A fully-executed (signed by both parties and delivered) Purchase Agreement is a contract. If the Buyer agrees to cancel the Purchase Agreement, you can both sign a Cancellation of Purchase Agreement form and the contract is canceled. If the Buyer will not agree to canceling the agreement, you should discuss the matter with an attorney.

-Dan.

You can always back out but there may be consequences depending on at what stage you are into the agreement. If the agreement is not finalized then you should be able to cancel right away without much problem. If not then there still may be a window of opportunity if there are unfulfilled contingencies to the agreement or during a counteroffer. It's best to review the purchase agreement documents you signed and discuss it with your realtor.