I looked at the pattern pretty closely and have a couple of comments.
You say, “the lace pattern is 11 stitches but it uses 13 because of the decreases”. The decreases in the lace pattern itself do not cause the lace to use 13 stitches but only 11. Or are you talking about some other decreases somewhere? You must have been working the lace over 11 stitches on the cuff because 66 will divide evenly by 11 but not by 13.
Just outside the lower left hand corner of the box that the second picture (the one below the chart) is in it says, “The 36 stitches on needle 1 and 2 will be held for instep.” I see the 36 stitches mentioned there but I didn’t see anywhere where it actually had you work over 36.
In the section “Gusset” at the end of the 1st paragraph it says
86 sts: 25 sts each on Needles 1 and 4, 23 sts on Needle 2, 13 sts on Needle 3.
And the next paragraph goes on to say:
While working instep, maintain first st on Needle 2 and last 2 sts on Needle 3 in stockinette st, while working the other sts on these needles in Lace Pattern. Sts on Needles 1 and 4 are worked in stockinette st.
If you divide the stitches up that way, 25 on needle (ndl) 1, 23 on ndl 2, 13 on ndl 3, and 25 on ndl 4, and then do what it says in that next paragraph it never has you working over 36 stitches. You will have 33 stitches that they didn’t designate for stockinette stitch. 33 works correctly for your 11 lace repeat to be worked 3 times.
I’m not real clear on all the parts of a sock (I’ve seen those diagrams where they divide a sock up like a half of beef and I always get bogged down.
) but I think the instep is the part of the foot on the top, opposite the arch of the foot and after you have worked the heel.
On that part of the sock you are keeping most of the stitches in stockinette and doing the gusset decreases along the edges of the stockinette and maintaining the center (of the top of the foot) in 3 repeats of lace, whose number is not messed with in this part.