Ummm..... jp) who? told you that a 130 ltr <85 cm wide board is enough to plane in < 12 knots?
Was that Jason Polakow himself?
You can stay with your 130 liter and you can "COMPLAIN" that you are not planing, or you can go with something < 90 cm wide and be ploaning on perhaps an 8.5 m2.
That's the physics here.
Yes, bigger fin will help you to plane a knot or two lower in the wind spectrum, but not a 48 cm.
Put a 60 cm on your 130 liter and you would plane earlier, but you would not like what it does when
your board gets up to it's full speed potential.
Your board is simply too narrow to work well with a => 60 cm fin.
So, the choice is yours.... wider board larger sail or not planing.