The watcher is monitoring a directory. Any file, regardless of name, will trigger it. In effect, you are looking in a directory named c:\Users\myfile\TestFolder\text.txt, and not for a file named text.txt in TestFolder. So change your query to this:
SELECT * FROM __InstanceCreationEvent WITHIN 10
WHERE targetinstance isa "CIM_DirectoryContainsFile"
AND TargetInstance.GroupComponent = "WIN32_Directory.Name=\"c:\\\\Users\\\\myfile\\\\TestFolder\""
and then you will have to do some other magic to get the name of the file that just landed.