I want to solve this by $\mathbf{PnC}$.

I know answer is $\mathbf 2$ only as I have verified it by drawing.

But with permuation, for $\mathbf 3$ we have $2-\textbf{choices}$ and for $4$ we again have $2$ choces.

$\therefore$ Ans $=2\times 2 = 4$

What's wrong here?