Need help determining if a multiwire branch circuit is wired correctly
Use a multimeter to measure voltage between the two hots (black to red). You should get somewhere around 240 volts. If you get 0 volts, the breakers are on the same leg. 

An empty service panel looks like this



I've drawn rectangles where breakers would go, and labeled the legs A and B. As you can see, breakers across from each other (left/right) are on the same leg, while breakers next to each other (up/down) are on different legs.

If you measured between breaker 1 and 2, you'd get 0 Volts. This is because they're on the same leg, so they're at the same potential. If you measured between 1 and 3, you'd get ~240 Volts. These breakers are on separate legs, so they're not at the same potential.