fk, i havent done banked tracks in ages
just to clarify, u take mv^2/r as a positive horizontal force towards the centre of motion right? so the net sum of the vectors pointed towards the centre = mv^2/r
i.e.
==> Nsin0 Fcos0 <== <== mv^2/r
wuld mv^2/r = Fcos0 - Nsin0