You presumably have an AZ jab. If so I would leave it for two reasons: Firstly there may be a knee jerk reaction on the schedules thanks to yesterday's letter (though that was entirely about first jabs incidentally) and secondly for AZ there is a lot of evidence that says "later the better" in terms of overall effectiveness. Pfizer does not have this evidence, in fact almost the opposite, so that's different, but in immune theory terms a delay ought to be better to spread the T cell timeline. One of the reasons why vaccine theory has tended to the earlier slots is purely human behaviour - in more boring circumstances if you leave 2nd dose vaccines too long, people just forget about them and don't turn up for the second dose - but I really don't think that is going to be a problem here. If your second jab is scheduled for close to 11 weeks AND you are past 5 weeks right now, then I guess there is an element of having nothing to lose if you cancel and rebook, but I wouldn't recommend it personally. You will get some slightly badly worded screens which suggests you didn't turn up for your appointment, but ignore those.