One comment I would like to add, from some women I met during my last two decades, talking to them online in the now defunct BF, and in Spanish sites, is that women should be very excited. Horny, is what I mean. Vaginas tend to enlarge when horny, and this should help to receive the large cock a dog might have.
As OP said, the knot will rearrange the inside of your body, and being horny will help you to make it smoother and less painful if it's too big or the cock is not in the right position. I haven't read or been told that vaginas also get wider when horny, so the knot should tie regardless of how horny you are if the knot it's the right size and in the right position to tie.
Don't hesitate to stimulate yourself before starting, like a preamble. Letting him lick your pussy will help, too.