They can sue you for specific performance. If they followed what they had to do in the contract and you did not, then they should win monetary damages.
Think about the predicament you put them into. If the shoe were on the other foot......
Do get a real estate attorney if you do not want to proceed.
Purchase agreements are legally binding. You could try and have a talk with them to see if they they will let you out.
They may or may not. You could be sued for performance or damages if you refuse to sell and there are no contingencies to let you out.
Best to get an attorney involved right away.
Or perhaps reconsider. There was likely a reason you wanted to sell. Has that reason changed?