No - new vines (stems) come from the base. It would have been more advisable to leave any growth that developed from that point rather than focusing on a single stem. This winter, I would advise pruning it hard - down to about 12-18" from the ground.

SAC is a VERY vigorous vine and can consume small structures without issue. I would have NO worries about it easily growing to cover your arbor.....and then some!! It just takes several seasons before that happens.

My SAC climbs from 6" to at least 15' up my deck, engulfing everything in its path, every year. I'm not sure why you want to restrict it to one vine unless you only want it blooming on the top of your arbor and not the sides, so I may not be of help here. If you just let it do its thing I think you'd get a lot more blooms for a lot less work, but if you want an opinion, I think if you pinched out the growing tip now, it would encourage more vines to start from the top and you could keep doing that for a while this summer to get bushier growth on the top. It is the kind of clematis that is usually cut down to 6" or so in the spring. For what it's worth, I think one year I didn't prune mine down, curious to see if it would add an additional 15' of growth to the existing 15', and I think it didn't - it just started from the ground anyway. I guess it depends on what you want it to do.

In my area, SAC easily reaches 25-30 feet - the late season equivalent to a montana :-) Mine grew up a 6' iron screen (salvaged from an old theater), 15' along a wooden fence and then up into a very large, old apple tree. A HUGE vine. It also developed a rather significant trunk diameter so there was a limit as to how hard I could prune it. Eventually, the best I could do was to the top of the iron screen. It still grew to the same dimensions each season.

I really like mine. It's nowhere near 30' tall, but still impressive every year.

My monster SAC in it's 3rd year now. Yikes!

Very nice kentstar! Thanks for the replies ...