Did you accidentally drag it to double layer? If the toolbar is unlocked, you can resize it like you would increase the height of any window. If that's not the case, you can right-click on an empty spot of the toolbar, select "Properties", and on the Taskbar tab, make sure "Use small icons" is checked.
The only other reason I think the toolbar would be distorted in size would be if you're running in a different screen resolution than normal.