I thought I'd responded to this. Geez.
I agree with Damian re the windex soak to strip the varnish.
Vallejo varnishes will work, but they are tricky to airbrush IMO (I've abandoned them even though Vallejo is my go-to paint). I do use the matt varnish for quick brush on touch ups. Other than that, I think there are other products that would cause you less trouble, especially as a beginner airbrusher.
I remember having some pooling and milky white issues with the stuff too. In short, it does appear that you've applied the varnish way too heavily. You need to spray it at 20-25 PSI (sounds high, I know), keep the trigger wide open or nearly so (if you are using a double-action brush) and keep that airbrush moving just as if you were spraying with a can. Don't stop, slow down, or reverse direction or you will get pooling. Start off the model, depress trigger, fan across and past model without pausing or stopping.
Folks will likely post opposing opinions that light several light coats are better, and they may be right. I've just never been able to make that work with any clear coat.
Good luck, you'll get this. I have found clear coats to be much more finicky than I'd ever expected. Don't despair, it'll come.