We may need a sketch to figure out what you are trying to do.
In the pic below, the top is the O42 turnout with O42 curves off the curved leg and O31 curves off the straight leg. The software measured ~ 7.5" center rail to center rail for that - not exactly what you state for distance, but close enough for me to wonder if this is the starting point of what you have now.
The second pic is with an O72 turnout, still using O31 off the straight leg, but also using O31 off the curved leg. The purple piece is just an additional piece of O72 drawn on top to demonstrate that O72 will not work for the inner part here, it will nearly hit the outer leg with only one piece after the curve.
The lower pic lessens the space between the tracks, but you seem to want more space between for a bigger station, not less, so I must be misreading your intent.
-Dave