Looks good.
By chance do you have any pictures on how you built the form ?
My only concern is that here in Buffalo our winters are pretty cold so it would have to built in such a way to hold up to our weather...
Sorry, no pics. Someday I will, but been saying that for years.
It's actually pretty simple. I generally pour the floor first and let that set up. That keeps the liner in place.
Then either set concrete block on the concrete floor or make a form and pour concrete.
To form I use 4 sides made of plywood with wood bracing screwed inside to form the walls. Pour concrete between the plywood and liner to make the wall. You can nail a piece of wood at the top of the form so the concrete will have a lip the skimmer basket can set into if you like. After it sets up, or even cures for a day I unscrew (pulling nails can crack the concrete) the bracing and tap the plywood forms away from the concrete. Have to be a little careful to not crack the concrete.
The weir I just form by hand, but another form could be used there. As you see in the picture I make the weir by free forming fake mortar rock.
If you like you can coat the concrete side of the plywood with dish soap as a release agent. Not really needed for such a small form.
I kept a pond in Kendell NY for about 15 years, about 70 mi to your NE. Yeah, winters, don't miss them. There is a seriously bad myth involving concrete, water and freezing. Water expands when it freezes and cracks concrete. In general this is false. For this to happen the the freezing water must be contained. For example, put a wide mouth jar, like a canning jar, filled with water into your freezer. Without the lid the jar will almost never break. Screw the lid on tight first and the jar will break every single time. The thing is that ice doesn't expand, it only takes up more space. So when a water module freezes it takes up more space. When the jar is open no problem air will be pushed out the open top to make room. With the lid on there's no place for the air to go to make space for the ice and the pressure grows until the jar breaks.
Now, an empty jar can crack when frozen, there are other stresses beyond water. But in general it won't. Same with concrete.If you look around Buffalo you will see concrete everywhere. Much of it will be sitting in water when it freezes but much of it will be more than 50 years old. When you see concrete falling apart it will be due to poor foundation, tree roots, poor mix, rusting rebar. Basically crappy building methods. But it isn't exactly because of freezing.
And besides, so what if the skimmer concrete cracks? It's inside a liner so it's not like there's going to be a leak. The structure will generally stay together and be useable for years. Don't use any steel reinforcement, that will cause problems. You can add a fiber-reinforcement material to the concrete, but that's really used so the amount of concrete can be reduced. I generally skip that and instead make 4" thick walls.
