Can I Extend My Non-B Visa in Bangkok If I'm Covered Under Amnesty Until July 31?

You are currently on a Non-B visa with a stay that began on February 16, which will end on May 15. Since you mentioned that you cannot do a visa run, you are inquiring about the possibility of extending your visa at the Immigration Office in Bangkok or whether you will be under amnesty until July 31. According to comments, it seems you will be covered under the amnesty, allowing you to stay until that date.