You might want to post to the Florida gardening forum. Up here in the mid-atlantic at least, the annual cultivars offered by nurseries have always struck me as finicky plants. Kind of like Gerberas that way. Only tolerating heat if they were kept well watered, had really good soil, and were partly shaded. I'd see people plant them and they would grow about 2-3 feet only, during the summer, if they weren't happy. Not sure if that's the case down there.
(and oddly, the Chilean/Argentinian M. laxa I mentioned in my other post, was quite vigorous here at least in spring and early summer, even though it should not have liked this climate as much as the tropical-derived annual Mandevillas. I feel like those have just been bred for huge flowers and nothing else. They want them to look good in the nursery so you buy them, but not be vigorous enough to last until next year, even if winter protected. But I'm pretty sure Florida is way too muggy and warm in summer for M. laxa)

I think there are more of the "bedding" type mandevilleas and dipladenias being developed that actually don't climb much.

It definitely should be climbing by now. I had a climbing one a few years back but lost it so I decided to buy another one. It was flowering and I assumed it was the same. When I got it home I read the tag and this one only gets a foot tall.