How do I unlock new courses in Mario Kart Wii?

I read somewhere online that in order to unlock a new course (or cup), you must get 3rd place or higher at the end of the cup. So I started up Mario Kart Wii and chose single player, grand prix, and 100cc. I then chose the cup I wanted to race. The race(s),(there are four) started, and I did very well. When all four races (the whole cup) were over, it went into the games little awards ceramony where I was given 1st place, but for some reason it didn’t unlock any of the locked/hidden cups. What am I doing wrong here?