I am not really sure you are getting an accurate evaluation of your calling when done inside your vehicle.
Calls sound a lot different on the outdoors....
If you can borrow a video or sound recorder try to record while you mimic the sound while you are beside the geese somewhere outside in a park or a friends farm where geese are frequent.
When you hear both you and the geese on the playback on the same sound track you should have a better evaluation on how your call actually sounds compared to the geese. It doesn't have to sound very close or exact, but the rhythm should be close.
The important thing is keep your welcoming call just that and not to sound like when they are sounding the Alarm.....
I hope this helps.....