Welcome to GT..
My first thought would be hand position.. fretting the string at a slight angle and when you lift your finger off the string heads back to its position.. Like most beginners you are looking to see that your fingers are headed to the right fret.. causing you to roll the guitar lower side away from your body. This forces your hand out of position.
Try raising the neck (approimately 45 degrees).. This will let your wrist wrap around the neck a little easier.. This may help until you get your finger tips broke in, your joints flexible and memory in place..
Also check back in fundamentals 1.. A picture is worth a thousand words..
http://www.guitartricks.com/lesson.php?input=13958&c_id=1&ch_id=2
Hope this help..
Good Luck
Gordon