“Is 3 days of antibiotics enough for pneumonia?”

Generally speaking, no. Assuming you are asking about an oral antibiotic, at least 5 to 7 days is the preferred treatment.

No, Pneumonia usually has a minimum coarse of 7 days of antibiotics. You should always follow your provider's instructions on antibiotic use. You should never stop your antibiotics unless your provider instructs you to do so. If you stop taking antibiotics before the provider instructed you to do so you are actually building super bugs in your body by knocking them down but before they die the antibiotic stops which gives the bugs the opportunity to grow immunity to your antibiotic. This pattern can result in making you very sick and in the future make the bacteria unresponsive to antibiotics.