Hi there! I'm new to this too, but I've been bugging the members here on Rootschat for a wee while now, and they are wonderful, helpful folks, so I'm sure you'll get some advice!
I'm at work with nothing to do and I forgot to bring my tree notes, so I took a quick look to see what I could find.
There are 3 William Jaffrey's that I can find that might be suitable (don't rely on this info, check it out!!) from IGI birth/christening extracts:
William Jaffray
bap 1772 Fyvie, Aberdeen father Alexr. Jaffray
William Jaffray
bap 04/06/1766 Fyvie, Aberdeen father Alexander Jaffray
William Jafray
bap 27/02/1769 Tarves, Aberdeen father Allexander Jafray
The first William might be a bit young to be fair but the other two look good. I only looked at Aberdeenshire of course, but Fyvie and Tarves aren't far from New Deer. How sure are you that the father is Alexander though, what are you basing this on? There are quite a few Jaffray's kicking about up there!
I also had a quick peek for Ann Burd and there are only 3 options coming up in that timeline, only one of them born Aberdeenshire:
Anna Bird
bap 02/04/1765 Methlick, Aberdeen father George Bird
I don't know if any of this will help, hopefully I'm not leading you down the garden path!
Lass x