Problem in a boost calculator circuit
The Maximum Repetitive Reverse Voltage of the 1N5817 is 20V and no-doubt your simulator will take this into account. This means that you cannot create an output any greater than 20V. Think about it - to generate 300V, that diode has to be able to withstand a reverse breakdown voltage of at least 300 volts.

Another problem is that in 0.5 msecs the inductors current will have reached 2.27 amps and you are expecting a 1A diode to pass that energy thru to the output capacitors: -

V = L di/dt therefore di = V dt/L = \$\dfrac{10\times 0.0005}{0.0022}\$ = 2.27 amps.

the 2.27 amps is the current attained thru the inductor when the MOSFET is switched on for 0.5 msecs - this current is then forced to flow thru the 1N5817 when the transistor open circuits. Clearly you are exceeding the limits on the diode twice.

Next, the IRFD110 is only rated to have 100V max on drain wrt source so you can never get 300V without damage. Also, with an on resistance of 0.54 ohms and an avarage current of maybe 1A when conducting, the losses are going to be noteworthy if not excessive.