This is definitely a non-standard core.
C x F = Ac = Area of the center leg.
3CM x 1.4CM = Ac = 4.2CM^2
240 VAC input x 1.414 = 340 VDC
You have a half bridge circuit so the transformer will only see 1/2 the bus voltage. 340 VDC/ 2 = 170 VDC
Primary turns = Vpri x 10 8th/4 x f x B x Ac
170 vdc x 10 8th = 17,000,000,000
4 = constant
f = frequency in hertz, at the transformer.
B = Flux, Gauss, do not exceed 1600 Gauss, general rule.
Ac = Area of the center leg = 4.2CM^2
Primary turns = 17,000,000,000/ 4 x 50,000 HZ x 1600 Gauss x 4.2CM^2
= 12.65 turns, use 12 turns.
Wind 6 turns primary.
Your secondary.
wind 2nd 6 turns of primary.
The two primary windings must be connected in series and in proper phase.
If you want to work with the equation yourself the only parameters you should change are the frequency if you want something other than 50khz and the Gauss which is the hardest parameter. Best guess 1200 for low Gauss and 1600 for high Gauss. Lower Gauss generally means cooler transformer, but then you need more turns.