Have you resolved this now?
Your window size is 854 by 480, and I was under the impression that the current maximum windows size width is 800px for the Arcade:
[quote:2n1hal2u]Upload your Construct 2 game file. The file must be in .zip format exported directly from Construct 2. All other file formats will be rejected.
Maximum size of upload is 10mb. Maximum width of the game is 800px.
Remember, this has no bearing on your Layout sizes, which can be as large as you like.