Hi.
You asked about your signature; although the image itself is smaller than the 350 pixel height limit, that limit refers to the signature in full, text and all.
Atm your signature actually falls above that 350 pixel limit with the picture and text (and so appears has having a scroll bar on some skins too).
So I'd suggest just fixing that up, say by removing some spacing/text or rearranging so it all fits. You can also use the Signature Rules thread to have someone let you know if your edited version of the signature is within the limits.