In the separation agreement, I agreed to sign over house to her. How do I reverse that so she can buy me out? And how much would it cost in NC?

While there may be a way to get out of the Separation Agreement, there is a very real chance that you are stuck with the deal that you voluntarily agreed to sign.  The Separation Agreement ("SA") is a contract between you and your ex, and like most contracts, you can't simply just say "oops, my bad, I want to get out of it."   If the proper steps were followed in the drafting and execution of the SA, you may not be able to get out of it and may have to comply with whatever the terms set forth.  You are going to have to schedule a consultation with a local family law attorney, but be prepared for them to tell you that there is little they can do.