It seems that a bunch of them spawn on the right side? I looked at your code and believe I have found the problem:
"addObject(coming, Greenfoot.getRandomNumber(490) + 5, 5);"
should just be
"addObject(coming, Greenfoot.getRandomNumber(400), 5);"
A new version of this scenario was uploaded on Wed Apr 17 23:54:46 UTC 2013
Not nearly done at all! I just wanted to show what i was working on when i made http://www.greenfoot.org/scenarios/8054
Hey @FlyingRabidUnicornPig did you download the source?
A new version of this scenario was uploaded on Wed Apr 17 23:57:16 UTC 2013
Not nearly done at all! I just wanted to show what i was working on when i made http://www.greenfoot.org/scenarios/8054
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