A very nice and elegant classical peice you have here. This would be great for piano students (I can just picture a little girl playing this, every once and a while stuttering for the next note

), but, just like others have said, it needs to develop more... it seems almost too short. You've written what can almost be a song. And in songs, 999 times out of 1000 (maybe more), you hear the main thought repeated in some shape or form as a second verse, and even a third verse (which could be repetitive here). I didn't hear the main theme ever again! I think if at :40, you used that arpeggio to lead back into the melody and add a "B" section, you could have a nice peice!
AND- it IS in B-flat major. You do use one G minor chord, but it dissapates quickly, and the peice doesn't end with it. So, it is in B-flat.
Now don't get me wrong; This peice is very good in more ways than one. Don't be discouraged, because you have the base for a good peice of music!
Alan