The only thing I could say is experiment with the height of the stool and lots of practice. You shouldn't be losing your balance. I felt that way when I first started and changed the stool height until it felt right for me. Practice, practice, practice.... You may need to change the pedal settings, but I'm not familiar enough with that pedal to help you. Maybe someone else could steer you right on that particular pedal. Sorry I couldn't be more help.   

Chair position could be the problem, but also posture and how much of the throne cushion your butt grabs. Experimenting with all of these will probably produce the optimum balance for you. Everyone's difference because everyone has a different inseam!

I agree with most of the responses already given.  It is not normal to lose balance.
The pedal is not the issue.  As stated before, throne and/or throne height, posture and the distance of the throne to the pedals is the probably cause.

I've seen a well known teacher describe how to set up as follows: (wish I could remember his name).

Optimally your height should be where your legs are slightly downward bent, ie, higher than a 90 degree angle.  Sit firmly in the throne, centered, not on the extreme edge.  Place your feet flat on the ground.  Your knee should be slightly behind your ankle.  Whereever this places the foot, that is where your pedal should be placed in relation to your throne. 

This was described as the position to obtain optimal leverage using the least amount of physical effort.  Of course everyone has their own preferences but this guy certainly knew what he was talking about and it is a good starting point.  I would hazard a guess that maybe your feet are positioned too close to the throne.

Scheming Demon sounds like he's right on the money.
The pedal shouldn't be the issue, but I'll say this, when it came time for me to buy a pedal, I considered the pedal that you are using, but was unsatisfied with the adjustments that it has.  I opted for the Tama Iron Cobra, it was more adjustable.

Definitely experiment with the throne adjustment though, it sure makes a difference.
Another thing (and partially why I passed by the pearl pedal) is the pedalboard angle.  It should be set to the angle that your foot swings out to when you walk.

You might be interested in Joe Stronsick's Ballistic Drumming technique. 
www.ballisticdrumming.com

It costs money, but he's also got a week of free email mini lessons that he'll do, so its worth looking into.  He'll send you a fee CD for a little taste, too.

I think Scheming Demon is right on as well.  I can tell immediately when my stool just the right height - which is about what he stated barring the small variance caused by people diffs.