685, You're doing fine mate.
What SS is getting at is theres a thin gear and a fat gear and sometimes people mix them up.
Later 17.5° tooth on the left. Earlier 15° on the right. I've seen a few mixed up and as SS says it's ok for a while but wears the intermediate and the fifth gear eventually. Theres supposed to be an X on each of the gears when they're all 17.5° but often there isn't. They also have a habit of putting the X on the layshaft on the inside face where you can't see it. When they're mixed up they do make things tight. To be honest the best thing you can do is whack the end casing with a rubber mallet. This will settle things down.