that's right! if you're just starting out with running i would actually recommend tossing the HRM for a fews months and just running for 30-40 minutes at a pace that feels "natural" (whatever that means)
as far as HRmax is concerned: that formula is not always very accurate. some people have hearts that can pump at a rate well in the 200s...i myself am sort of a diesel-engine: i pump slowly.....from experience i would think my HRmax is in the 180ies...