Need help with Square 20 of Learn to Knit Afghan

[OldGreenMare]

I'm working on Barbara Walker's Learn-To-Knit Afghan, and am on Square 20, "Scale Quilting." Here's where I'm getting stuck:

Row 6: With color B, k2, *sl 3 wyib, k1, insert needle from front under loose B strand of Row 1, and knit next st, k1; rep from *, end sl 3 wyib, k2

I assume I'm inserting the right needle under the strand, and that I knit 2 times after picking it up...then I have

Row 7: With color B, k1, p1, * sl 3 wyib, p3; rep from *, end sl 3wyib, p1, k1

Now I'm starting to doubt my Row 6, because how do I purl 3 when there are 4 things to purl? I tried purling the middle two together, but it didn't come out looking like the picture. Do I just let one drop, maybe? I'm getting tired of starting over. Has anyone done this who can walk me through in more of an "I'm talking to an idiot" kind of way?

Thanks!