Doubt one's booked (11)
I believe the answer is:
reservation
This clue is a double definition.
'doubt' is the first definition.
(to have reservations is to have doubts)
'one's booked' is the second definition.
(as in booking a reservation)
(Other definitions for reservation that I've seen before include "Expression of doubt (about a claim)" , "Expression of doubt; table booking" , "misgiving" , "Booking (in a restaurant)" , "Qualification, proviso" .)