You should call now and ask the phone agent to note it on both reservations. Room assignments at resorts occur a few days in advance, so now is the time they'd be taking that into consideration. Call the regular Disney number, provide both confirmation numbers and ask them to link the two and note that its a continuing reservation and you'd like to keep the same room. When you arrive for the first reservation, the front desk should be able to let you know if you will remain in the same room for the second reservation. With occupancy being low, I wouldn't expect it to be a problem now as long as its the same room type booked.