I think I might have screwed myself up, because I got all of the 119 stars and saved the 120th star to be the star given to me after beating Bowser in the Sky - but only after beating the game and getting that star did I realize I might not be able to save my game with the 120th star because the ending screen with the cake never goes away, and after I reset my game I found that once again I only have 119 stars.
Did I ruin my chances of ever getting that 120th star on that game file? Or does the big star at the end not count as a star at all, and I'm simply missing a secret star? I'm a bit confused.
Oh, first let me tell you that you're really in the wrong place. The DS version is updated to have 150 stars, and the N64 board is probably more active than this one.
But to answer your question (which you did yourself), that ain't the star you're looking for. Try to pause the game to the in-game pause menu, or check the stats from the file select screen. There you can see what you're missing. You should have 6 + 1 hundred-coin-star from every course, plus an additional 15 "castle secret stars". One should be missing from that list --- "You're a jerk, Dent" Wowbagger from The hitchhikers guide to the galaxy