I don't grow it, but the one I observe is pruned back to around 40"' in spring and it makes a nice full shrub.

Now that you've thinned it, I say leave it alone. It will send out more canes without your needing to treat it like a floribunda. In future, keep in mind that it is a good idea to get in the habit of removing a few old canes (3 years or older) every year on large shrub roses, including rugosas. That way the rose is always rejuvenating itself without your needing to take it down to the point where you're at right now. And Michael is right: you can take it down in height if you wish, too - in future. You've probably done enough to it for this spring anyway. (But I wouldn't try to make it too short; one third reduction is enough or Fru Dagmar might sulk as she did for me when I got a bit carried away one year. My fault, not hers - I should never have planted her so near the back steps.)