No, you are not.  The point in discerning a vocation is not that you become a priest, rather the point of discernment is to help you figure out and become the person that God created and calls you to be.  If you have been thinking about a priestly vocation, the best way to really discover if you have a vocation is to enter the seminary.  Most men who enter the seminary today are not sure if they really are called to be a priest or not, but it is a possibility that has been on their mind and so they enter the seminary so that the system that is in place and the advisors who are present in the seminary can help them identify what God is calling them to do with their lives.  During the years spent in formation, God's will for you becomes clearer as you pray and discern with others.  Even if it should be discovered that you are not called to the priesthood, the time you spend drawing closer to God and becoming the person you were created to be will pay a lifetime worth of benefits.

If you were to enter the seminary right out of High School, it would take you a minimum of 8 years to become a priest (about the same amount of time as it would take you to become a doctor!) so there is a lot of time available to you in the seminary to discern.  Even if you come into the seminary with a college (Bachelor's) degree, most likely you will not have completed all the prerequisites necessary to enter Major seminary and thus you will have to take 1 or 2 years of "pre-theology" in order to qualify to get into a Major Seminary, this means that even if you've had a lot of education you will still have a lot of time for quality vocational discernment. 

With modern communications and technological advances we can get information and accomplish a lot more work in a day than was possible years ago.  But despite all those advances, the way discernment and learning to understand God's call has not changed.  It still takes a good amount of time and patience to discern God's will.  When a man enters the seminary, as time goes by he learns more about his heart and God's call for him will become clearer. In that process, if he decides to leave the seminary that doesn't mean that the discernment process didn't work, in fact just the opposite - it means that it does!

Because there is a shortage of good priests today, it is always hard to see a bright, talented man leave formation.  However, the blessing of the process is that when a man reaches the point where time has come for him to make permanent vows, he can do so with the assurance that if he wasn't called to the priesthood that reality would have surfaced by that point.