Re: Need help.
A transistor with 0.6u length can never be a good current mirror, as its output resistance is quite low. So if you want good mirroring, use large lengths ( ~2u) or use a cascode configuration.
There will be a lot of discrepencies with the simple square-law model and the simulated result. The best way to choose transistor sizes and overdrive voltage is by plotting the current for various combinations of width/length and using it as a reference. But anyway, for a given overdrive voltage, the ratio of widths should match the ratio of currents flowing through it, provided they are both in saturation.