This happened with the 7700 when it first came out. Janome outsources most of their website work, and hasn't updated it just yet. I would suggest just sitting back and waiting to register for a month or two. Warranty is not an issue, because all of them are obviously in warranty at this point. Also there may be goodies offered on registration (e.g. the O2 1/4 foot for the 7700) and if you register too early you might get lost in the shuffle and miss out.

Hi, I am trying to register my machine online, but I don't see it listed
on the registration screen. I have emailed Janome about this, but if
anyone has any suggestions, let me know. (I'd rather not rely on the
mail for this.) Thanks.
Joy