To get True Wizard you must collect enough studs in a level to fill the bar at the top, the easiest way to get True Wizard is to utilize to score multiplier extras for 2, 4, 6, 8 and x10.
These are found and bought in the Hogwarts hub world but you can use cheat codes that are input upstairs of Wiseacres Wizarding Supplies in Diagon Alley in the Leaky Cauldron hub area and then turned on in the pause menu under extras:
Score x2 74YKR7
Score x4 J3WHNK
Score x6 XK9ANE
Score x8 HUFV2H
Score x10 H8X69Y
Once these are turned on every stud collected will be worth x3840 so True Wizard will come with the first stud collected.
Note: Once you have earned True Wizard you can save and quit.