The jam signal or jamming signal is a signal that carries a 32-bit binary pattern sent by a data station to inform the other stations of the collision and that they must not transmit.
Means sender already knows that collision has occurred than only he send Jamming signal to others.
Our motive here to let sender know about collision, which he already knew before sending Jamming signal.
So don't count Jamming signal time while calculating frame size.
Frame size must be = 208