Although I much rather that you wait until you can see a dentist to evaluate the tooth and re-bond the veneer, I also understand the anxiety and potential embarassment one would go through spending an entire weekend without a front tooth/crown
So I will offer you a suggestion to temporarily address your problem.
The solution involves some Super Glue/Crazy Glue (or perhaps "Gorilla Glue" though I've personally never heard of gorilla glue).
First, you'll want to make sure you know how the veneer fits back into position. So get yourself a mirror, and practice placing the veneer back into position properly until you're comfortable with where it's suppose to be.
Then, if possible, you'll want to get a pair of thin latex glove, but a well-fitting one. The reason I'm recommending wearing gloves is that Super Glue + skin = instantaneous bonding. This would be great if you wanted to bond the veneer to your fingertips (which we don't).
You'll also want to get some cotton balls or gauzes and strategically place them under the lip but away from the tooth structure. This is to keep your lip (again, skin) from potentially coming in contact with the Super Glue.
Once you've done all this, you can proceed with dabbing 1 (ONE) small drop
of the super glue in the middle of the veneer. Carefully handle the veneer and align it with the tooth and apply gentle, but firm pressure for about 30 seconds.
If done properly, then the veneer should stay put long enough until you're able to get to your dentist for a proper exam, evaluation, and re-cement
If you're uncomfortable with ANY
of the steps mentioned above, then I highly recommend hiding out for the weekend, stay home, and wait until you're able to see a dentist on Monday morning. However, keep in mind, this solution is temporary at best. The veneer and the tooth structure needs to be properly "treated" in order to provide optimum bond strength.
JulXXXXX XXXXX, DDS