How should I learn Mandarin?

So, I have been taking a Mango language class through my local library. I thought I was picking up the correct pronunciation!?

Well, when I try my new skill on a Chinese person, I am very courteously corrected for my mispronunciation which I welcome with fervor.

I walk away confident that I am now ready to try again. When I do, on a new victim(because it is surely nails on a chalkboard), I speak in the way suggested by the prior native speaker.

Strangely it seems I am corrected each time. To my great confusion I have found myself in the middle of an argument between dialects.

What is to be done? I am resolute on learning Mandarin very proficiently. (Dating a chinese girl is not in the tea leaves, and was already suggested)