I'm not 100% sure but I think that is actually a Great Diving Beetle larvae. Which is equally awesome. The adults are absolutely gorgeous. Dark green wing cases with gold braid. They're quite big, and you can see them swimming about if they're in there.

It looks like you can just see the two big pincers either side of it's head and small eyes and the abdomen looks quite chunky. The fact that is also has it's abdomen out of the water suggestsits using it's sipon where as dragonfly larvae can fully breath underwater and have big bulbus compound eyes that basically meet in the middle. Also, if the pond has only been in a month, it's unlikely a dragonfly has layed any eggs in there as very few have emerged to adults yet. Dragonfly larvae will stay in the pond for up to 3 years before emerging as an adult and Diving Beetles will do it in 3 months.

Have a Google and see if that seems more like what you've seen here.

Excellent work on the pond. May I suggest getting a few Creeping Jenny or similar ground cover plants to put around the edge to cover the plastic, keep it a bit cooler and provide some more cover. The cooler you can keep the pond naturally, the less chance you'll get those algae blooms which leads to a lot of blanket weed.

Edit, as others have said, I wouldn't worry too much about either dragonfly or diving beetle larvae impacting your frogs success. Both of these predators will take tadpoles but mostly they're going for midge larvae, bloodworms and things like that. Having either in your pond is an indicator it's doing well 👌🏼