Before we start, a note: If you haven't already, I'd recommend stay stitching the neckline and armholes now that all your bodice pieces are assembled. Do a line of stitching at a 1/2" seam allowance all around, to stabilize the curves around your neckline. It's best to do this directionally, starting at the top of the curve, and always ending your stitching at the lowest point of a curve. This keeps your pieces from stretching from being stitched in opposing directions.
Okay, time for your straps. Remember how we taped the two strap pieces together? So you'll just have two long strips for both the front strap and the back loop.
Now I'm going to show you a different way to sew the straps rather than stitching and turning them, as in the pattern directions. I'm going to turn in the straps and edgestitch, which means no turning is involved. Yay!
Fold each strip in half lengthwise and press a crease.
Then turn in each side to meet the crease. Use the tip of your iron along the very edge of the fold so you don't press out your first crease.
Edgestitch along the open side. I use my #10 Edgestitch Foot for this.
Finished straps, no turning involved.
Okay, take your pattern piece and chop off the ends where you joined the two pattern pieces.
Now get rid of one of those pieces; you only need one!
Now cut that remaining piece in half to get two small pieces. These are your back strap loops.
Thread a ring onto each small loop, like so:
Okay, the next part required a video to explain. It's a but tricky to see (and to do on camera) but I hope it makes sense.
Attach that little bit to the strap using a zipper foot so you can stitch close to the slider.
Finally, attach the end of the front strap to the front bodice just like you did for the back bodice, centering over the mark, with the strap facing down.
There you have it: fully adjustable straps!