Most home bleaching systems cause some degree of sensitivity the severity of which varies from individual to individual.
The best advice would be to attend the dentist. I am not entirely sure about that particular system but with many it is possible to use the trays on for example alternate days, this usually will reduce sensitivity but slightly prolong treatment time.
I would recommend the use of analgesics and possibly topical application of a sensitive toothpaste, being very careful not to swallow it.