Thank you all for the kind words of encouragement and advice.
I've finished the 12 squares for the swap. I may have to add a border to get them to the required 12 1/2 inch size but I'm ok with that. I have done some practice with seam allowance and have found that moving my needle position over one tic to the right gives me the correct seam allowance.
I know I can do this - just have to remember that Rome wasn't built in a day and quilters don't have perfection for a very, very long time - if every. De-stashing sale is cancelled!