Urgent! webinar in 2 days and need to upgrade capacity plan

Hi support team, i am on the annual plan webinar with 1000 capacity, and my plan will expire in middle Dec. I have a scheduled webinar 2 days later on Aug 29 and NOW the registration is over 1000  and keeps increasing. I like to upgrade the capacity to 3000 just for this Aug 29 event, and like to know if the 3000-capacity upgrade can be done in time and if it can be purchased just for 1 month. Look forward to your reply, Thanks!