You could also try just showing up early the first night of class. Sometimes people don't show up and if you are one of the fist ones there, you can take their place. In PA the classes fill up very quickly so this worked for me.
do this...sign up for a class for whenever is convienient. If you have to wait just show up for another class if you have the time. most of the time someone doesn't show and the spot will be yours. show up early because a lot of others do this. i've did this twice when the first class ended up not suiting my schedual and i got in another class 2 days later just by showing up.