Good for you for scheduling an appointment with a doctor.
I do not think it is safe to say that there is a 100% chance of your having cancer. You should never try to diagnose yourself. There are a few different things that can cause lymph node reactions.
"Essentially 5 broad etiologic categories lead to lymph node enlargement (Ghirardelli, 1999).
* An immune response to infective agents (eg, bacteria, virus, fungus)
* Inflammatory cells in infections involving the lymph node
* Infiltration of neoplastic cells carried to the node by lymphatic or blood circulation (metastasis)
* Localized neoplastic proliferation of lymphocytes or macrophages (eg, leukemia, lymphoma)
* Infiltration of macrophages filled with metabolite deposits (eg, storage disorders)"
emedicine.com/ped/topic2975.htm
Sometimes it is actually not serious or life threatening, so don't worry yet. You can't worry before you know for sure what the issue is!

Good luck. Let us know what the doctor says. When is your appointment?