Your attorney was present, the mediation sounds normal enough (five hours isn't excessive), and you signed the agreement knowing that you were giving up your interest in the house. If you didn't want to do that, then you should not have signed. You should have read it "slowly and clearly line by line" at the time of the mediation--not afterward. I hope that people who read this question and answer learn something from your situation. "DON'T BE IN A RUSH TO SIGN A MEDIATION AGREEMENT." You can always get the mediation agreement drawn up, then tell your lawyer and everyone else that you want a couple of days to think about it--after all, there are real estate transactions that give you three days to get out of the deal, and a marriage deserves the same consideration.
I'm afraid that you might be stuck with the agreement you signed. Your best bet is to get a new attorney to help you try and get out of this mess. Good luck!
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.