A lot of people get similar results. Saving gas and increasing MPG is all about smart driving. After being a member of this forum for just a few days I've read so many different ways to help increase MPG and non aggressive driving is almost always the starting point. Along with that you may want to inflate your tires to a higher PSI b/c that has been showen to up fuel efficiency as well. Just keep searching the form and you'll learn all types of different tips.
By your description, you should have gotten far more than the 10% gain that you got. I would expect at least double the gain you described, and if you were actually driving aggressively (vs. normally) before you should have seen absolutely huge gains.
Perhaps the miracle water-for-fuel stuff you're selling on your website is holding you back. You might want to perfect that for your own use before trying to make click money on it.