My guess is it won't ever heal to sufficient strength, these annual plants generally don't live long enough, just a few months. I suppose you could use grafting tape, which is kind of like wax, but I'd want it under the zip tie, and I don't think it'd be a good idea to remove the zip tie at this point. Your fix seems good enough, now watch and wait and see if the branch continues growing. You might need more leverage, another tie, string, or wire up several inches higher also holding the branches together.
An alternative would be to snip it off, or even snip the main branch below the split node, then retrain remaining branches as desired, but yeah you lose some growth and associated regrowth time. Good luck.