I have a cr-10 smart, and when I print every time, the first layer is not coming out right. half of it is printing great, and then the other half is so thin it's barely visible. I have leveled the bed but don't know how to adjust the z axis as it says to do in the instructions (of course, it does not show how). do I need to have the bed or hot end heated when leveling? if so, what temperature?