Block #7 is the most fussy to piece thus far in this sew a long.
Some info that may aid you:
With smaller pieces thread quality can make a difference in the accuracy of your piecing – a good reason to always use high quality thread. – Example: Aurifil 50/2 is 50 weight and 2 ply, the higher the weight number the thinner (finer) the thread. When stitching smaller pieces I find I have better success with a finer weight of thread and a finer needle 75/11 or 80/12. A stitch length of 2.0 to 2.5 is best. Happy sewing :)
Or find block #7 here