It looks like when you moved the yarn back to front or to the back you took it over the needle instead of between the needles. That adds extra sts and will throw you off. Moss stitch is knitting what look like purl sts and purling what look like knit sts on the row you're doing, so maybe you need help identifying what they look like. This sticky thread
has some pictures. There's also a video for seed st (same thing more or less) on the Tips page.