not visa related but you'll probably be needing 10 visas before (If ever) your bike is registered here. I suspect you never had good advice before you shipped it here.
Depends which immigration office you are using. Some are 45 days before, some are 30 days before, Jomtien for instance are 15 days before but can be 7 days before at busy times
if you haven't made an appointment, you need to post the documents and passport.
You had an option to make the appointment but you somehow missed it. Go back into the system and see if you can schedule an appointment but I think it's too late now.
You go too the Embassy on the day you made the appointment with your printed Bar code slip and give them the documents and your passport you uploaded. They will then give you a day to go back and collect your passport