Should I be worried?

I visited the Cincinnati Flower and Garden Show three or four year ago and while I was there I bought a few plants. (I don't think I've ever gone anywhere and not 'bought a few plants!') Anyway, one of the ones I came home with was gooseneck loosestrife (Lysimachia clethroides). The vendor told me that the plant was vigorous to the point of invasiveness, but I was taken with the slender, tapered flower heads, which do indeed remind me of a goose.

I planted it in less than ideal conditions (dry, just part sun) to try to limit its spread and I must have done a good job because it hasn't moved an inch.

I don't know if that should make me happy or sad.

If it's really a bear to keep in bounds once it takes off, I guess I'm glad. But as it stands, the plant is beginning to make me doubt my ability as a gardener. If I can't even grow a vigorous-to-the-point-of-invasive plant, I may be forced to turn in my Master Gardener patch...