The reason the holster was a little too loose was, you're wrapping the gun in plastic when you mould it.
You should NOT do this, since the thin layer of plastic is JUST enough to make a loose fit.
The right way is to "case" the leather by soaking in water or alcohol, then let the leather stand until it returns to it's natural color, but still feels slightly cool.
MOST people try to mould while the leather is still too damp.
When you think the leather is about right, insert the BARE gun into the holster and mould it to your satisfaction.
Slide the gun out, which will cause the holster to open up slightly, then press the leather gently back into the right shape and allow to dry.
If you had the leather cased to the proper condition, the gun will be bone dry.
All you'll need to do is wipe it down with a little lube on a patch.
More suggestions:
Investing in a few more tools will boost the appearance and quality greatly.
You can buy these tools at Tandy leather either in a local store, or online.
An edge beveler tool. #3941-03--Size 3.
This cuts a bevel on both sides of an edge to give a smooth, rounded edge.
An edge "slicker". #8122-00
This is a small wooden or plastic wheel with a groove around it.
Use a fine round file to open up part of the groove to a larger groove that will fit thicker leather.
This tool is used to put a shiny, slick finish on the edges of the leather, which gives it a much more finished appearance.
Gum Tragacanth. #2264-01
This is a slimy substance that's applied to the raw edges, then the circle slicker is briskly rubbed over the edges to give it a hard finish.
After this you can either dye the edge a darker color, or apply a wax and buff with a coarse piece of canvas to give the edges a final finish.
A edge creaser. #8072-00
This tool comes in different sizes or an adjustable model, or you can make your own.
This tool is used to impress a shallow line or border around the top edge of the holster and on the sides of the snap straps.
This also gives a much more professional, finished appearance.
A stitching groover. #8074-00
This adjustable tool cuts a shallow line in areas where you're going to stitch.
This makes a much more even stitch line, AND buries the stitching below the surface to prevent wear.
In addition, the stitching has a more even appearance.
A stitching spacer wheel. #8079-05--Size 5
This is a spur-like wheel that actually marks the location of stitch holes when you run it down the groove cut by the grooving tool.
This comes in stitches per inch, but I find the #5 or 5 stitches per inch the most useful.
A diamond awl. There are several running from $15. to $25.
This is the tool used to actually punch the stitching holes.
The diamond shape's edge is aligned with the stitching groove, and this causes the stitching to pull INTO the leather instead toward the edge.
Another option for thinner, single layer stitching are drive-type Diamond hole punches.
These punch from one to 4 stitching holes at a time.
Single, #8065-00.
4 prong, 1/8" spacing, #8067-00
GOOD stitching cord, waxed or you can wax it with beeswax.
This is rather hard to find, but it looks much better than the waxed Nyltex cord you're using.
That cord is flat, and uneven.
Good stitching cord is round and very even, usually white.
There are several options. I'd ask Tandy for a small sample of each of these, and you can decide which you like:
White polyester cord, #3959-04 or 3959-05.
Sewing Awl Thread, #1205-03.
Nylon thread, #56275-003.
Tandy also sell cakes of beeswax so you can wax the cord, if necessary.
Egg-eyed, blunt tip stitching needles.
Also know as harness needles.
Size 000, Large is the most used, #1192-13
A stitching book. #61944-00 or #61906-00
This shows how to use the above tools and get much better looking stitching.
HOW you orientate the diamond awl and lay out the stitching determines how good it looks, and how strong it is.
Last a professional leather finish to seal the dye in, protect from moisture, and give it a shine.
For this, many pro's use Fiebing's Resolene. #2270-01.
This is an acrylic finish that looks like milk but drys to a clear, hard finish.
This is probably the best all-round finish because it doesn't crack, chip, or peel off like most of the others.
You can apply it with a damp cloth or a spray gun, then force dry it with a hair dryer.
These tools and material will make your projects look like a professional job.
You're already most of the way there, all you need are a few tools, learn how to use them, and a little practice.