No there's 10 courses in total, I guess your talking about the 3 courses you play in the Castle Club?
They're the main bulk of the Castle Club part of the game, the rest of it is just practise modes, a shop to buy (upgrade) your Mii and a nine hole one on one putt challenge.
There's much more content in the Quick round option on the main menu, that has all the Challenges in.
The 10 courses are:
Forest Course: a forest-themed course where multi-colored hills can be seen in the distance.
Seaside Course: a beach-themed course with a similar appearance to Blooper Bay.
Mountain Course: a desert-themed course with multi-colored cacti.
Those are the 3 you play in the Castle Club and are not part of the Mario Universe so to speak.
Then there's the following:
Peach Gardens: a Peach's Castle-themed course, with pink fairways and greens.
Yoshi Lake: a course with many pools of standing water with a resemblance of Yarn Yoshi and some levels of Yoshi's Story. Unlocked by collecting 7 Star Coins in Challenges mode.
Wiggler Park: a flower garden course with a Mega Goomba and other giant characters. Unlocked by collecting 14 Star Coins.
Cheep Cheep Lagoon: an underwater course with Cheep Cheeps and and other marine creatures. Unlocked by collecting 21 Star Coins.
DK Jungle: a Donkey Kong Country Returns themed course, featuring Screaming Pillars and Barrel Cannons. Unlocked by collecting 28 Star Coins.
Bowser's Castle: a Bowser-themed course, with many Bob-ombs which will explode if contacted. Unlocked by collecting 35 Star Coins.
Sky Island: a par-3 course set in the sky, where clouds and Para-Beetles can be seen. Unlocked by completing the nine-hole One-On, One-Putt Challenge in Castle Club mode.
These are in the Quick round option mainly but you also get challenges in the Castle Club on them to win special items.