Can I visit friends in the US for a few days on my C1 transit visa?

Your C-1 is a transit visa, and not intended for visits, as outlined by the US State Department

Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa, either a nonimmigrant visa for temporary stay, or an immigrant visa for permanent residence. Transit (C) visas are nonimmigrant visas for persons traveling in immediate and continuous transit through the United States en route to another country, with few exceptions. Immediate and continuous transit is defined as a reasonably expeditious departure of the traveler in the normal course of travel as the elements permit and assumes a prearranged itinerary without any unreasonable layover privileges. If the traveler seeks layover privileges for purposes other than for transit through the United States, such as to visit friends or engage in sightseeing, the traveler will have to qualify for the type of visa required for that purpose.

It goes on to provide, as an example (emphasis mine):

A foreign citizen traveling to another country who will have a brief layover in the United States when the only reason for entering the United States is to transit.

And, further, the example of what is not allowed:

A foreign citizen whose layover in the United States is for a primary purpose other than to transit, for example to visit friends or sightsee, requires a visitor (B) visa.

As your destination is Jamaica, it would be disingenuous to use a transit visa for a stopover visit and may do harm to future visa application credibility.