I frequently bike through a wooded trail on my own, and thankfully have never encountered any problems, but I can understand your concern. Is there another path that is in a less secluded location, such as alongside the roads you'd take to get to work? Another option would be to take the bus if your city has public transportation.
I always bring a small whistle that I wear around my neck when I go biking or hiking by myself, and slip it onto my key chain the rest of the time. The whistle is lightweight and ear-piercingly loud, and if I was hurt, lost or approached by a creeper, I could easily grab it and blow to get the attention of others and scare him off. Ask your parents if there is a whistle lying around the house that you could use. Also make sure you bring your charged cell phone with you. Avoid making eye contact with anyone, and simply keep biking if someone acts suspiciously. If you are wearing your iPod, make sure the volume is low enough so that you can hear those around you.
It's awesome that you already have a job at 14. I hope you have a safe ride there and back tomorrow, and a lovely birthday on Saturday.
~ Pax / Peace : )