It is possible he could sue you and get a judgment and get a mechanic's lien against your property. It seems clear you had some sort of contract with him for performance of a service. While you view his skills substandard (and believe me I get that), you may have to convince a small claims judge or jury that you are correct. In general contract terms, you can't cancel a contract for performance in the middle of the performance. Having said that, this guy may be so annoying and unskilled that this is your only practical remedy.
You now have 3 options:
1. Do nothing and hope he goes away.
2. Look at his documents, see what they say, sign them if they don't compromise you in any way, and pay him $220.00.
3. Pay him $440.00 so there is no argument.
My best guess, based on what you've said (and it's just a guess, but an educated guess) is that option No. 2 will work best for you.