I wired like directions say and the fan and heater don't work. What have I done wrong?

I have no idea. More information needed.

I used a single pole breaker that alows 2 wires to connect to. Ran black and red wire from aiw 12 cable to breaker. Then black to black and red to red on the heater. Could this not work because the two ac lines are not 180° out of phase?

Something is wrong here, not to state the obvious.

How do you have a single pole breaker connected to two wires?

What voltage does the heater need? 120 or 240 ?

A single pole breaker only allows for 120 volts, need a two pole breaker for 240 volts.

If you used two single pole breakers, they must be directly next to each other in the panel to get 240 volts. And if you used two single pole breakers, it must be changed out to a two pole unit, for various reasons.

Or you may have used a tandem breaker, looks like a single pole as it uses only one breaker slot, but allows for two 120 circuits, it has two separate handles. If so, then again this must be changed out to a two pole 240 volt breaker.

A photo of the panelboard interior showing how you connected wires to the braker would be helpful.

Sounds like you have a single pole breaker that has two circuits on it. This still only gives you 110 volts. You probley need 240 volts to your heater. Make sure you check this. You should consider having an electriction hook this up.