How do I change the margins in the arcade?

I uploaded a game to the new Scirra Arcade, and it has come out as an extremely small frame. I don't know how/where to change this. Any help would be greatly appreciated!

Thanks

Tom has created a thread for issues with the new arcade, so probably best to post such queries in that section.

Here: https://www.scirra.com/forum/new-arcade-beta_t129648

Thanks, I didn't even see his thread in all my searching.