Top Down Insertion in a B Tree
It seems you are doing nothing wrong. Like you say, for a B-tree of order $n$ the number of children is between $\lceil n/2 \rceil$ and $n$, the number of keys is one less.
For $n=5$, keys are between $2$ and $4$. When you add a key to a node of size $4$, you get two new nodes of size $2$ and one new key which is pushed upwards. When this happens at the root, a new root with a single key is formed.

Your example. Add $T$ to the tree. At the root $G$ go right, to $\{H,K,N,Q\}$. With $T$ this becomes $\{H,K,N,Q,T\}$ which is too heavy and we split into $\{H,K\}$ and $\{Q,T\}$. Middle key $N$ is pushed upwards to the root. In the new configuration the root $\{G,N\}$ with two keys has three children $\{A,C,E\}$, $\{H,K\}$ and $\{Q,T\}$.