Bent wrist

So just started learning guitar and singed up for guitar tricks but im having a problem with the spider exercise on that my wrist is bending alot when trying to get my finger tips on the string and the more i try to stretch for other frets it seems to bend more, im also finding alot of tension on my wrist and im having to push my thumb into the back of the neck just to make the stretches,so my question, is this normal while building up strength on my fret hand or am i doing something completely wrong?

Just to add i do have small hands and shot fingers

What kind of guitar are you playing on? Since you have small hands, you would probably benefit from playing on a really thin neck like Ibanez's Wizard neck or even Super Wizard.

But then again, I think anyone can adapt to any guitar. But in general, your wrist should be pretty much straight with your forearm. It should bend a bit when fingering certain chords, but for the most part it shouldn't bend too much. So pay attention where your thumb is on the back of the neck. This is the rule of thumb I try to follow:

http://www.pbguitarstudio.com/pdf_files/GUITAR_PDF/Classical_Form.pdf

Here's what not to do (keep in mind for both of these links that some of these rules can be bent for certain things. For example, sometimes you'll need to flatten/collapse one of your fingers to mute other strings or for certain chords. So use common sense with these links):

http://www.pbguitarstudio.com/pdf_files/GUITAR_PDF/Bad%20Technique%20Page.pdf

Hope that helps!