How do I beat the Banana Cup in Grand Prix(150cc) On Mario Kart Ds?

I was playing Grand Prix and after I finished 50cc and 100cc version,so I started On 150cc.Let’s say I passed all the cups exepct for Banana.Of course I can’t go to the leaf cup or the one after that ‘because I have to unlock it by doing the Banana Cup.

Of course I’m stuck on that 1,the tracks it has are: Donut Plains 1 Frappe Snowland Bowser Castle 2 Baby Park

so thats all you have to do on that one…So heres my story: I skipped along marally on my DS to play the Grand Prix on mario kart ds, and I clicked grand prix and went on to 150cc (the three mushroom one) and clicked the Bannana peal.picked my person and went.In the first course(donut plains 1) I got a 1st place, on the second one(frappe snowland) I got a 2nd place( I think this altered the rank.But On the other cups before this one I've gotten E's and passed with 4th place,2nd place, 3rd and 2nd!),on the third bowser castle 2, I got a first place, and on the last (baby park) I got 1st. I got a C as a rank and won the movie that it plays at the end with 1st scnd and third. So It didnt unlock anything.There I sit with a c rank banana trophy cup, and I've re done it with almost-perfect scores and I havet unlocked the Leaf Cup!! Ugh!

~somebody help ill do anything for you ANYTHIN~