I have a 2 CM nodule and smaller nodules in my lungs. Will be getting a pet scan. How quickly will it spread if it's cancer?

Depends. Cancers spread at different rates. Small cell cancer spreads quickly. Treatment also affects the rate of spread. If the pet scan is positive next step is biopsy.
Lung nodules... Rate of spread depends on the type of cancer. Lung nodules can be from primary lung cancer or metastases from other types of cancer outside of the lungs. Lung nodules can also be benign/inflammatory/infectious in etiology. A 2 cm nodule should show up on pet scan but smaller nodules may be below the resolution of pet. Serial scans will determine if the nodules are stable, growing, or resolving.