I am currently in a Scratch camp and we are working on making a maze game. However, we are running into some problems.
1.) When we control the ball using the arrow keys, the ball is first jumping to the side before moving in that direction.
2.) We have programmed the ball to return to the start position when it hits the walls, but it is going through the wall instead. We set it to go back to start when it touches a color. It seems to work in other posted Mazes, so not sure why it's not working for us.

Here is the link to the project: http://scratch.mit.edu/projects/24476710/#player

I have an answer to your first question that might help with your second question too
The costume for the ball sprite is off center. When it points in a direction, it rotates around that center. To center a costume, go to the top right corner of the costume-edit screen and you will see a button shaped like a cross. Click on that and you will see a big cross though the screen. You can move that around the to center of the ball.

Hope this helps

You can find out maybe by looking at a similar project I made:
http://scratch.mit.edu/projects/24496714/