Regarding lining up problems. Make your approach the way your instructor tells you to. When you are about to make your turn from base to final, don't try to line up with the center of the runway. Instead, position the plane in the air to be in line vertically over the INSIDE edge of the runway and try to keep it on that line as you get closer to the runway. When you get over the runway you will most likely find your plane very close to the middle using this method.

Try to make your base turn to final at an altitude that lets you see both the ground under the plane and the plane itself. Meaning to not be so high that all you see around the plane is sky. The hardest part of using this technique is mentally extending the edge of the runway out to where you are making your base to final turn.