Don't take my word for it, but: I assume that since 12U and 12L are a single continuous piece of metal, it doesn't really matter from an electrical point of view. The division is done to keep things tidy.
While waiting for a response from the real circuit wizards here, you can always check your resistances and see if everything checks out. You could also re-check the rest of your connections, keeping an eye out for cold joints while you're at it. Just don't plug in the amp until you get the go-ahead from someone who actually knows what they are talking about!
