Ok I just searched ravelry for this sweater and apparently everyone in the Big Girl Knits forum had gauge issues. Even using the yarn called for in the pattern. the way people worked around it was one of 2 ways, either changing the needle size or just continuing the last color until the desired length before starting the ribbing. Another continued the chevron pattern in the desired length before the ribbing. Oh and ignore the row gauge. I hope this helps.
So this was no way your fault. EVERYONE had issues.