This will give you the experience that most recent college graduates don't have. This will put you in an even more select group of recent graduates. You will be required to write reports and other documents, and to present your ideas to the people who will pay for the ads. If your writing or presentation skills are not of professional calibre, you will not survive in this profession. Take the criticisms of your written class assignments seriously.
Mistakes are alright.
You can't know everything, but try to learn from your mistakes. Several of your classes will require you to present your work, so take that opportunity to practice and learn from your mistakes. In the advertising profession you must be able to stick by your convictions when you meet with a client. Remember, you are being hired as an expert, and so are expected to give expert advice. Clients that want someone who will do only what they think should be done, don't need an ad agency.