Overs and Unders

At my maths class today, we looked at probabilities, and I recalled a simple boyhood gambling game called Overs and Unders.

It involved tossing 2 dice simultaneously, and we could bet on:-
- "OVERS" where the sum was over seven. (which paid even money 2:1)
- "UNDERS" where the sum was under seven. (which paid even money 2:1)
- "SEVENS" where the sum was exactly seven. (which paid 3:1)
According to my primitive calculations there are 36 possible outcomes from tossing 2 dice - 15 of these will be "overs" and 15 will be "unders" and 6 will be exactly "seven".
This would mean that it is better to bet on sevens because the expected return is better than on either overs or unders.
Am I on the right track?  Does it mean that you have a 50% chance of winning on "sevens" as opposed to only a 42% chance of winning on either overs or unders?