Add Transylvania (Not quite Kentucky in OTL), proposed colony of Vandalia / later proposed state of Westylvania (Not quite West Virginia + Eastern Kentucky in OTL), and Charlotiana (Roughly the Northwestern Territory of OTL just after American Independence). Perhaps Plymouth stays as the OP stated, keep West Florida separate with both Floridas being admitted, and divide New Jersey in two as had actually happened once already by that point. Maine, Vermont, and Upper Canada could have their own governments as a price for supporting independence while Nova Scotia, New Brunswick, Prince Edward Island, and Quebec are brought into the new country by conquest or of their own initiative. Should Bermuda and the Bahamas be brought into the new country as well, you now have 27 polities instead of 13.