dependencies not working both ways

I’m having problems with the dependencies.

For example, I have main products A and B. A has 2 options and B has 3 options. In step 1 you choose product A and in step 2 you choose B.

If A1 is chosen, B1 and B2 will be visible and B3 will not. At A2, all 3 options of A can be seen.

But if someone first completes step 2 and chooses B3, then I am left with both options in step 1. How do I ensure that the dependency also works the other way around?

Or is there a way to make step 2 inactive until step 1 is completed?