I pruned the main branch of my (7') weeping willow tree last year too low (I'm guessing) and now the main branch is about 3-5" off center. The tree is now about 12-14' high.
Is this a problem? If so, how do I correct it?
Now that there is a photo to work from I feel confident that this is not a problem. Yes, it probably would have been better to leave a leader but with the fast growth willows have one branch will end up becoming the new leader. I think one of the side branches is already tending upwards. It just needs a little help. See here for corrective pruning practices which include
replace it by splinting an upper lateral on the highest scaffold to a vertical position. Prune all laterals immediately below the new leader. Use wood or flexible wire splints, removing them after one growing season.
In general you should follow these points with weeping willows (Salix babylonica):
Something else to keep in mind is that weeping willows get quite large (20–25 m or 66–82 ft). They have brittle wood and drop branches all the time. This is not a plant you want close to your house or near anything that can be damaged by something large and heavy falling on it.