K3 + bind off 8 = 11sts, which you will repeat 5 times (meaning 55 sts and 4 sts to end of row=59sts you start with).
The pattern repeated 5 times means you should end up with 19sts on the needles, with 40 bound off.
(K3x5repeats=15sts + 4sts at end of row=19sts left)
(bind off 8x5repeats=40sts gone.)
When you bind off, your 3rd stitch disappears and the 8th bind off leaves 1st, so you still have only 3 sts with each repeat. Don't count the 3rd st as part of your bind off, you need to K1 to start your bind offs. So K the 4th st then pass the 3rd st over it as the 1st bind off.
When you do the first K3, bind off 8, the first 2sts and the 12th st will be the 3 sts on your needle. With your next repeat of K3, bind off 8, you'll K the 13th, 14th, 15thsts, then K the 16th st (to start your next 8 bind offs)and pass the 15th st over the 16th........
Hope that makes sense!