The same happened to me the night before my mum's wedding and I couldn't fix it in the dark on my own. In the daylight I was under the van covered in grease and fixed with half an hour to get a shower and dressed and be wedding transport!!
My gearstick came out as only the rear bolt was tightened to any degree, the front bolt was sitting loose which enabled the gearstick to move and work the rear bolt loose. Can you get all other gears satisfactorily, and does it drive ok in all gears?
At a risk of stating the obvious have you made sure the pin in the ball at the bottom of the gear stick lines up with the cut out in the cup of the shift rod? I had to lie underneath while a friend moved the gear stick until it was all in position then quickly put the bolts in without moving anything - then check its all still in line before tightening both bolts up fully.
Good luck 8)