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If you have booked a flight only, it should specify the actual flight, and in this case information from the airline should be sufficient (if your booking is "confirmed").
It would be different if you had actually booked a package (flight+hotel), as they could possibly switch you to another flight, but in this case you would generally not have been informed of the flight number.
Have you tried using the Thomson Airlines website's "Manage my booking" feature? It should let you know everything about your booking.