Super Mario Run only has 24 levels. Well made, hand-crafted, perfectly replayable levels, of course. But that's still not a huge number.
There are three more that you might not have played, though. These are super special bonus stages only available to most hardcore and dedicated Mario fans.
The first level requires you to get all 120 pink coins. There are five pink coins in every level in World Tour, but you'll need to get all five in one go to keep any of them.
Your best strategy is to play the level and look for the coins, and then play again and try and get them all. If you miss one, hit the bubble icon to go backwards and try again.
Once you have all 120 (you've been busy!) go to the shop in the kingdom builder, go to the special section, and buy the Pink Coin Pipe. Now tap on it on the kingdom screen to go to the new level.
Once you have all the pink coins in a level, you can replay that stage and try to get all of the purple coins. These are harder to collect and may be hidden inside blocks or in tricky out-of-reach areas. More practice and skill needed.
Get all 120 and you can buy the Purple Coin Pipe, like above.
Finally, grabbing all five purple coins in a level gives you access to black coins. These are even tougher and some require certain bonus characters. You'll have your work cut out for you if you want all of these.
But get all 120 and you can access the Black Coin Pipe and try the last bonus level in the game. Good luck!