You should find the following in your World class:
super( x, y, px);
x and y represent the width and height of the window. Use a higher number there and the window becomes larger.
This is an issue with my computer. I tested at school's computers, and it worked nicely.
In my own computer at home, the window is smaller and I get vertical and horizontal scrollbars
2013/6/7
2013/6/7
2013/6/7
2013/6/7
2013/6/9
2013/6/9