NCAA rules: 6) Stepping toward second base without completing the throw is legal if the base is occupied by a runner or there is an attempt to retire a runner.
2) The “spin” or “open” move to second base is legal if the pitcher raises the lead leg and immediately, with a continuous motion, steps directly toward second base. The pitcher need not throw.
You can step off or try the spin move to second base without completing the throw at any level.