There's no reason why you should allow it to grow straight up and straggly, as all you need to do is cut it back. As a shrubby plant it will make new growth and new flower heads on those new shoots. There's lot of time to do that and get a good show of flowers during the summer.

I found the same as you Mousy. Bought it last summer, put it in a bigger pot and it bloomed, and I shortened it and it bloomed again, and got chopped again and it is in bloom now, and the bees love it, but it's like its on stilts!! It will have to be discarded as it looks too leggy. There is another one queueing up to take its place but this one is reluctant to bloom.