If you load a G code  file into Mach3 and there are extra circles in the tool path that were not part of the program, you are likely in Absolute IJ Mode rather than Incremental IJ Mode. You can correct that two ways. First, you can change your default setting in Mach3 by going to Config>General Config and change the setting it in the IJ mode box. The second way to address the issue is to add a G91.1 in the begining of the G code file. This will leave your default setting as is, but ensure that your G Code file is run with the setting it requires.