I forgot!

I forgot to write in my journal for two days.
I was very very sleepy.

On Saturday, I went to the stadium to cheer up  ON Ehime university baseball team. 
I played the trombone hardly .
Though we had  lost the game, I think I won the support of the crowd (他の件名は大丈夫). I had a great time.

-- 

よくできました！楽しそうですね。

I had forgotten!

I had forgotten to write my journal for two days.
I was very, very sleepy.

On Saturday, I went to the stadium to cheer up the Ehime university baseball team.
I played the trombone hardly. [Did you play the trombone a lot? "I played the trombone hard." or did you not play very much? "I hardly played the trombone."]
Though we lost the game, I think I won the support of xxx {you need to clarify this: whose support was won?}. I had a great time.

My remarks:

I turned your last sentence from the past perfect [we HAD lost the game] to a simple past/preterite, because a past perfect tense always requires an older action in reference. So the introductory sentence [I had forgotten to write my journal] indicates to your readers that the story takes place AFTER those two days of no journal writing.