Impedance matching (RF transformer) - Impedance dependence
I'm using a TC2-1TG2 1 to 2 impedance trasnformer. I want to convert a
50 ohm load to 25 but I'm finding that the transformer only works for
50 to 100

If you want to impedance match a 50 ohm source to a 25 ohm load then you need to step down the voltage and not step it up. Try operating the transformer in reverse to how you connected it in your tests i.e. primary = higher number of turns and secondary = lower number of turns.
Your turns ratio for 2:1 impedance transforming should be \$\sqrt2\$:1.
Alternatively, if your bandwidth is limited, use an L-Pad impedance transformer.