I recently purchased a 2004 Giant Cypress SL w/ 19" frame. I am 71" tall w/ a 30" inseam. I tried some of the frame size formulas, but they were too complicated. Now that I have rode the bike for a week, it seems like it might be too small. I have the seat raised about 6". The riding position on the bike has me leaning forward quite a bit. The bike also has a pretty steeply angled top tube too.
I'm 5'11" and ride a 20" frame and find it to be about the size I want, though it supposedly a bit to big for me the bar rides up into my nuts. I like it, and the smaller 18" specialized frame I looked at I didn't like....that's just my amateur opinion. if it seems to big try adjusting the saddle, that made all the difference in the world on mine!
I have the Cypress SX in a size 19" which is the same frame. I am 69" tall with similar inseam. This bike, though in the Comfort class, seems to lean the rider forward more than other bikes like the lower Cypresses. It's more in the flat bar road bike class, or Speedbike class. I like that personally.
You chose a great bike and I suggest you keep it. There are a number of things you could do if you want a more upright posture:
--replace the stem with a higher rise one, or buy one of those adjustable stems so you can dial it in over time
--replace the flat bars with riser handlebars.
Since it's so new, you could probably get your shop to swap that stuff out for next to nothing.
When the pedal is at the furthes point (just in front of the bottom), if you put your heel on the pedal, your leg should be absolutely straight. This give the approx correct knee bend with the front of your foot on the pedal. The rest is trial and error making small adjustments to the saddle position until it feels right.
The leaning forward might take a bit of getting used to, but will eventually make riding more comfortable as it will take some weight off your butt and put it on your pedals.