Sounds like a simple clutch cable adjustment.
Most all new builders underestimate the amount of pull and/or movement necessary to fully disengage the clutch.
My advice, do not start messing with the right side (flower nut) until you understand what you're doing. It is rare that the clutch needs adjusting from factory settings. It does happen but not often. Usually problems like yours can be fixed by a proper cable adjustment.
As was suggested above by Maurtis, Adjust the cable so there is no slack when the handlebar lever is not depressed. Any slack in the cable betwen the clutch actuator arm and the cable holder will cause the clutch to remain engaged even with the handlebar lever depressed (squeezed).
A simple test will tell you. Disconnect the cable from the clutch actuator arm then depress the arm inward, toward the engine, until it stops. This might take some effort. There's a strong spring to work against. While holding the arm in try to spin the rear wheel. If it spins free your cable is too loose. If it doesn't get back to us. There is more we can offer.
With that said it has been 2 days since the OP asked for help with no response.
Tom