This is currently glitched... in a good way. There are 4 courses in each theme, each with 3 difficulties. The difficulties don't stack, so you have to play each course 3 times. You also have to progress through all 4 courses on Easy, then all 4 on Normal, then all 4 on Hard.
However, this is currently unlocking as soon as you finish the 12th Giant Home course (the 4th Hard course). You don't have to play through the other 2 themes right now. This may be patched, so take advantage of it while you can.
The Hard difficulty can be frustrating at times, but there's usually a trick to it. A lot of times that means avoiding most of the course and shooting straight for the hole.
If one of your opponents gets a hole-in-one on the 1st hole and you don't, you might as well just start the course over. In addition, if you have to take a 2nd stroke but you can nab the purple gem with one more, it's better to do that. (2 strokes = 8,000, 3 strokes + gem = 7,000 + 2,000 = 9,000.)
Do *NOT* restart just the hole, or you cannot win the tournament. I also tried to quit out of a hole that I was doing poorly at, but it reset the course.
Hope this helps!