Umm... ?? Jackmanii is pruning group 3. It should be cut all the way back every year.

It will be fine.

Give it some organic fertilizer such as well rotted manure, alfalfa pellets, compost or Rose Tone to give it a boost.

What you did was not a problem. It will grow up from the roots with more vines than before with more flowers. Jackmannii should be cut back hard every year.

Those love a good haircut every year! The jackmani I inherited with this house had several years worth of neglect, and boy, was I nervous when I cut it down to the nubs. Big sigh of relief when I saw the new shoots, and it went crazy up the trellis and into my gutters!