I have a 2014 Honda Civic SI and it won't go into gear when the car is on but will when the car is off definitely clutch but anything else?

Car won't go into gear when it's on

What else would it be but the clutch?

It is not the "clutch", it is the clutch release mechanism. Either you have a failed hydraulic cylinder and or low fluid. There's a slight chance of the residual pressure valve being bad, but that is internal the slave cylinder I think. Of course the clutch line might be broken too.
Find the reserve tank for the clutch fluid, top it off and "pump" the clutch. This might solve the problem for a little while.
As a side note:
When the actual clutch fails the engine will race when pressure is applied to the gas pedal. A failed clutch slips and yours is not slipping- the pressure plate is not being pushed back so the transmission can be disengaged from the engine.

It may not be the clutch. A bad slave or master cylinder will cause the clutch pedal not to work.

Clutch is shot. BUT check the slave cylinder first and check if it is pushing the clutch fork when the pedal is pressed.