Hey milly, thanks for playing. Did you encounter the bug where the enemy doesn't attack? If so, that would explain the ease, and the work around is to drag the map icon onto your sc2 exe icon instead of using "test document."
If the attack wave triggers DID work, then keep in mind that the game is defaulted at normal difficulty. There is no way I know of to change the difficulty at the moment. Upon the game's release, however, there will be 2 more difficulty levels. :)