A child is generally not going to be charged with a CRIME for being a runaway, but the people that aid and assist said child can be. Plus, being a reported runaway will result in an entry in a national database that can be discovered as part of a comprehensive background check later in life. Further, a child that runs away can eventually be deemed as incorrigible and MAYBE a motion can be brought by child services or others to place the child into state custody.
A lot of things MIGHT happen. What WILL happen will depend upon your specific circumstances and what your parents do when you take off.
WHY will you be running away? Who will you be taking off to rendezvous with for these three days?