Sorry about no responses here guys!
Ya it's within the limits.
And when I check it in Paint, it is 350 pixels. Did I miss something?
You could try setting the text to a certain size, because sometimes on different styles the default text appears larger, or even on different resolutions (not sure if you did that tho, and can't really check right now).
By the way this thread is only for staff to reply to, just because if all members reply it could get chaotic and people could be fed the wrong information, which wouldn't be helpful to the members who do want signature help.