It's always that first row that gets me too... 😅 This is awesome though, love to see nalbinding content on the fedi!
Personally, what I've been doing instead is using a thin knitting needle as sort of a stand-in for my thumb, like this. That gets all the stitches nice and tight! Probably kind of a cop-out to just learning the "proper" way to get good tension, but it works.