Is saying "i am free of social anxiety" a good affirmation?

Yes, and...: Affirmations are a great tool. "Fake it til you make it" & "act as if" are useful, but other things are best added to that to make it stick. In gradually increasing ways, acting on these statements is very powerful. So if you talk to @ least 2 people a day (can only be saying hello to two people passing on the street to start with) & keep increasing, the feelings will change also. Good luck!