For starters, don't use those screws.
Here are some tips:
(This is one of the most useful – Tape the bottom of the bag, eliminating corners that fish can wedge themselves into.)
Bag Preparation
The key to success is to plan ahead. Don't wait until the last minute for anything. Make sure that you have your bag, rubber bands, oxygen supply, boxes, tape, insulation, packing water materials (Sea Salts, AmQuel, Antibiotics), have the fish cleaned out, substrate and decorations cleaned, and capture nets or cups.
Bag Preparation
The bag should be minimum 2.5 mil thickness. For the larger, spinier fish like Surgeons, Triggers, etc., we used a triple layered 3 mil bags.
Different kinds of fish need more or less room in a bag, and more or less water. Keep in mind that it isn't so much the "water" that ensures a good "ride" for the fish, it is the column of O2. Most fish will do well in a bag that they can comfortably turn around in, depending on the length of the trip. Just enough water to keep them covered while swimming upright, plus and extra 1/2" of water in the bag is all that is needed. However, for larger more active fishes, like Wrasses, Triggers and Groupers as examples, they need more water coverage.
Make an "envelope" of newspaper, using about two or three thicknesses, to put between the bottom 1/3 of the bags. If a fish spine pokes through the first bag (and this happens alot), the newspaper will help stop the spine from going into the second or third bag, helping to retain the water. Even Wrasses can poke through a bag. Their pectoral fins contain a sharp spine. The other thing to consider are fishes that have sharp teeth, like larger Wrasses and Triggerfishes. Many times they will try and bite through a bag, so the use of a newspaper liner is wise.
Tape the bottom of the bag, eliminating corners that the fish can wedge themselves into.
Use Oxygen when you gas your bag. It might sound difficult to find, but it isn't, really. Nearly all shops that do auto work have an acetylene torch. You can use this quite nicely. It won't be "hospital grade", but we used this kind of O2 for years with great success.