I don't think you can do anything to fix it a couple of my games had the same problem
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Your sprites are way too wide and they shrink when uploaded to the website. Make your sprites 480 by 360.
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At one time all costumes and backgrounds were limited to 480x360 and were automatically scaled when read into Scratch. A change (perhaps a bug) was introduced in v1.2.1 that allowed big sprites to be created, but the Java version did not support this change.
It is unclear whether future versions of Scratch will support big sprites officially, or go back to limiting all costumes and backgrounds to 480x360.
There are a lot of good reasons for supporting bigger images, especially as scrolling backgrounds, so I hope they embrace big sprites rather than going back to the original limitations.
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http://scratch.mit.edu/projects/NobodyKnowsNorune/104649
My project didn't work and it has nothing to do with costumes, I has spent hours working on this and I made it perfect! It worked shamelessly then when I up loaded it, the health bars didn't work, the exp bar didn't work, the sprites took no damage and the music wouldn't play!
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its because you use a sprite bigger then the screen. when it goes online it reduces itslve to normal size.
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Well if Heybrian is right your problem is sloved
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