I have a lip laceration from surfing. How can I boost my immune system instead of taking amoxicillin?

Why amoxicillin. A laceration is not necessarily an infection, and in the absence of any evidence of overt infection you should not be taking amoxicillin. Unless you have some underlying disorder of your immune function it does not need "boosting", if there is such a thing. Let this heal normally and do not take unnecessary medications.