I just played the game, it was simple and charming, I'm guessing you only have one mission because after the message of "mision 1 complete" appears, nothing else happens. I found two small issues, the first being that you can leave the screen by the sides and the other being on the tree minigame where you can jump infinitely and fly (that one is a bit funny).
the only things I would recomend changing are. putting the name of the game above the play button at the start. making that after you are done talking with the clouds you can see the background image (the ones where claire talks to the clouds) and chanign the dialoge bod for the same one but HD (I bet it was small and you just made it bigger, i've done that).
anyway, i liked the game, I hope this comment doesn't sound harsh.
about the UI i don't know exactly what you mean but if it is the game page size you go to edit page -->embeded options, there you chose to have teh sime adjusted automaticaly changted or manually, if manually go to -->Viewport dimensions, and there you choose the size, the default is Width 640 Height 360. other thing related to pageand thatare on meta data -->promo images and there you have many things