2N2222 low side relay switch not turning off

So before pressing the button voltage measures 6.9V. Press the button and voltage difference drops to 0.25V. Release the button and voltage goes up to 6.5V – Bananaman 20 mins ago

Given that your supply is 12V it should measure near 12V or near 0V between collector and emitter. The 0.25V is good, but the 6.9V and 6.5V are not.

Either your 2N2222 is connected backwards or it is defective, check that it is oriented correctly and/or replace it with a new one.

From the photo it looks like you have the transistor backwards this may have damaged it.

I think the power supply is good. An inverted transistor behaves like a 7V Zener. So the current flows through the relay allways, which is not enough to pull in the relay. The reversed transistor also has a current gain (reverse beta > 1). The base current increases the emitter current and pulling the relay. After that, the relay remains switched on, because the holder current is less than the current flowing through the 7V Zener.