You can try, but it won't work for sure. The 'Free play levels' are just that, a list of all playable levels. This included the deeper dungeon maps, but all
custom maps you download will shop up there as well.
You really should be able to scroll. You'd have to figure out why it won't work,... are you sure you're clicking the correct location?
If the button doesn't work, perhaps there is a problem with the resolution,.... You could try to install the
latest nightly, or clicking somewhere next in the list to see if that won't work.
If all else fails, you could try to temporary delete the maps you've already completed from the \KeeperFX\levels folder, so the maps further down the bottom show up.