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Simple and short.  I feel like you could have kept the 2nd section after the repeat in G major as it clearly wanted to stay there instead of returning back to C (and that part near the end where you try to force it to go back to C sounds artificial imo) and then you could have reprised the original idea from the beginning and made it into an A B A' three-part form.  That's just my take on this piece though - it's up to you as composer to decide what's best of course.  Also, when I personally have such short ideas I resort to writing variations to easily lengthen my piece.  Thanks for sharing!