transformer design

I am busy designing a transformer with the following specifications:
a 1:1 transformer -
a planar type transformer - made on mulitlayer PCB
12A rms continous current in both primary and secondary.
resistance of winding must be as low as possible - less than 3-4 milliohms
frequency can be anywhere between 150-400kHz.
input/ output voltage is 8V peak to peak square wave - i.e. +-4V
as small as possible
core loss should be 100-400mW
I have followed the guide given by Ferroxcube and came up with the following calculations. It seems to me that my primary turns is way to little.
Will anyone please comment on this and evaluate my calculations?
Results of core calculations
E-E14/E-PLT14 3F3 material Ve (mm2)                300/240 Ae (mm3)                14.5 Maximum core Loss Density (mw/cm3)    1095/1225 Maximum Allowed Flux Density (T)    0.16 Primary Turns            2.182
E-E18/E-PLT18 3F3 material Ve (mm2)                960/800 Ae (mm3)                39.5 Maximum core Loss Density (mw/cm3)    612/670 Maximum Allowed Flux Density (T)    0.125 Primary Turns            1.005
E-E14/E-PLT14 3C94 material Ve (mm2)                300/240 Ae (mm3)                14.5 Maximum core Loss Density (mw/cm3)    1095/1225 Maximum Allowed Flux Density (T)    0.188 Primary Turns            1.864
E-E18/E-PLT18 3C94 material Ve (mm2)                960/800 Ae (mm3)                39.5 Maximum core Loss Density (mw/cm3)    612/670 Maximum Allowed Flux Density (T)    0.151 Primary Turns            0.844
Thank you
Johan Wagener
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