I'd like to reiterate for page 2... playing 2 balls is really not an etiquette issue. If/when the course is backed up, playing 2 balls is not uncommon, especially for a single or twosome. What is an etiquette issue, however, is driving a ball into the group ahead of you.
I see from your profile that you are pretty much new to the game and that you're an educated person, so instead of beating you up about it, I'd just like to instill a bit of golf etiquette on you... let's make the right decisions on the course from now on now that you know how big of a deal this selfish and dangerous act was.