I have Dell Inspiron 14, using USB external soundcard with GS3. The external mic works but the internal laptop mic will not turn off. I can go to Devices and unenable the internal mike but that makes no difference when I go into Audacity. It still records both the internal and external mic.
Normally, Windows only records from one “thing” at a time.
Make sure you select the USB mic as your Recording Device.
You may have selected “loopback” or “stereo mix”. Those record what’s coming out of your soundcard and that can be a mix of inputs.