Screen resolution - Help!

Hi there - I am new on macs and when I lent on my macbook pro this morning, it changed the screen setting and I dont know how to get it back to normal! The screen looks like I have plugged the VGA thing in to go to my data projector when I use it at school. ANY help would be greatly appreciated as I have a heap of work to do on it this morning and the screen is bugging me....

Thanks heaps!!
PennyPea

 

Thank you SO much! Im glad it was so simple....

So you know what the default setting is?

 

OK - thanks again. So appreciate it!!