It is not. 1-1, 1-2, 1-3, and 1-4 are all different levels. In case you're confused by the menu, there are only two spots on the map, but you scroll down on a spot to access the different levels within. To that same end, I should also mention that if you're stuck on a level, there's a win condition. Most levels just require you to get to the end, which is denoted by a little cave/altar looking background piece. (Press Up to interact with it and clear the level, obviously.) There is one that requires you to kill a certain amount of a certain type of enemy, which you'll be able to notice based on the number that appears in the bottom corner. Just watch for when the number goes up and you'll know which enemy to take out.