Seaming 2 bound off edges

I am knitting a Barbie dress for my grand-daughter. (I can knit, but not really confident on assembly…) The left and right backs, as well as the front, are bound off edges. It says to sew 5 stitches into the shoulder seam. What is the best way? I’ve tried it a dozen times - a dozen different ways - and am just not happy with the look. I guess I want a NICE seam. HELP! Just not sure how is the neatest way to sew 2 bound off edges together.
(I know it’s just a Barbie dress, but I am a perfectionist…)

Thismight help. Also, there’s a video of some seaming techniques elsewhere here at It’s toward the middle of the page. Hope this helps.