People with certain conditions have been offered three doses as their primary shots and the a fourth shot as a booster.
I'm not sure if that would cover you or not, but it sounds like that kind of scenario.
19th is good - keep it.
I've only just found out my 76-y-o mum and 68-y-o aunt haven't been invited yet (by Strand Medical in Worthing).
It's difficult to find any appointments this side of Christmas and many involving travelling from Worthing. In fact, there is nothing locally here at all.
I can't verify this myself as an already triple-jabbed old man, but I hear that the booking site may now accept over-30s booking their booster.
So, if you're 30-39, it might be worth a try before it's officially announced...