What bearings have you fitted to the car? original roller bearings with the centre spacer seperate or the V-taper type with the built in spacer?

the outer race of the bearings should but up to a shoulder on the inside of the hub assembly and when fully assembled with the drive flange c/v etc etc there should be no sideways movement.........unless you have the bearings with the built in spacer on the inner race (V- taper type bearings) which can foul each other and cause this said movement you are talking about but it shouldn't be 20mm, maybe up to 5mm side ways movement especially when the drive flange/c/v nut has been tightend up.

Have you by chance forgotten to fit something to the assembly such as the tapered washer and or flat washerbefore you fitted the c/v nut?

have you got a drum brake c/v and drive flange instead of a disc brake c/v and drive flange?
Hope some of this info helps.
Cheers Scott