I'd say that is a good guess. Not that I ever even heard of ruellia, lol, but I just googled it and the photo looks very similar to yours. Pretty little plant! Is it aggressive or behaved?

:)
Dee

Almost certainly some form of plumbago, aka leadwort, aka Ceratostigma plumbaginoides. The spikey centers to the clusters of flowerlets are a dead giveaway.

Here is a link that might be useful: Hardy plumbago, from Dave's Garden