Sew a gathering stitch along the top edge of the 2" knit fabric strip. To make a gathering stitch, change the stitch length on your machine to the longest possible stitch (usually a 5). Sew a baste stitch along the entire upper edge, without stay-stitching the ends. Then gently pull the bobbin thread on both sides so the fabric gathers in the middle.
Overlap the ruffle by simply folding it over on itself and bringing it up at an angle. Allow the bottom edge of the next line of the ruffle to cover the upper edge of the previous ruffle line. Pin in place. Repeat so the ruffled lines gradually get larger with each line as you make your way to the neckline.
If you still have ruffle to spare, like I did, bring the ruffle over to one of the shoulders. Pin around the neckline, until you reach the shoulder seam. Then repeat the layering ruffle process backwards, layering the ruffles smaller and smaller until you reach the sleeve. Cut off any remaining ruffle.
Use thread the same color as your ruffle knit fabric to carefully sew a zigzag stitch along the top edge of each ruffle layer. Make sure to only sew the ruffle to the front of the onesie, not the back. Starting from the very bottom ruffle line, the smallest, lift up the next line of ruffles so as not to catch them in your stitches, and sew the top gathered edge. When you reach the edge of the ruffle line, where you turned the knit fabric, stop sewing. Bring the next ruffle down, and start sewing the top edge of that line using a zigzag stitch. Repeat for the entire ruffle all the way around your onesie, stopping and starting at each new line.
Cut 2” off the end of your scrap fabric and set aside, this will be your bow center. (Alternatively, you may use a 2” piece of coordinating color scrap fabric for this). Fold the 8” piece of scrap fabric in half right sides together, pin and sew along the outer edge. Turn tube right side out.