You say that normally when you write a piano piece, you give up half way through because you don't really know what you're doing. So, what to do next? Well, rather than treating this piece as a finished article, treat it as the skeleton of a finished article.
What I mean is that you've got here something that by your own admission is not entirely interesting or challenging, but it could become something much more interesting if you take it and try modulating to different keys, you do already vary the rhythms a little here and there and changing the left hand up every now and then, but keeping the whole thing in the same key is really not good.
have some fun with it and see what you can do.