Did you allow enough chain stitches to allow for them being used as the first stitches in your return row?
I swear by YouTube when I trying to learn something new.
It has been my constant companion since starting DD's waistcoat.
I have to admit I never make a swatch to check my tension/size, I know I crochet tight so I always use a hook one size bigger than recommended.
Also I usually make scarves and blankets so they tend to end up whatever size they end up.