Bronchitis and antibiotics

I've had a bad chest cough for about 2.5 weeks. I went to the GP today and he prescribed me antibiotics. My sputum (when I have it as the cough is often dry) is white and does not appear too unhealthy.

I took one pill today without reading up on bronchitis but now I feel that it might be caused by a virus as I have other cold symptoms and recently had a cold sore.

Should I finish the 5-day course of antibiotics? I've only taken one pill and I regret it already.

Thanks