Need help in designing a BJT Amplifier with Avnl = 100
There are a bunch of problems with your circuit. Your collector is at 9.5 V and your emitter is at 5.3 V. I would expect the output to swing between -3.2 V and 2.5 V having 1 V across the collector emitter to keep the transistor biased. You need to bring the emitter voltage down to about 1 V. Put your Q point at half the supply voltage.

Your decoupling capacitor is too low for 300 Hz. The 50 uF capacitor has an impedance \$X \approx 10\ \Omega\$. This will decrease your gain significantly. Even worse, the impedance is frequency dependent. So the gain will change with frequency. If you decrease the biasing current, it will have less of an effect, as the resistors will all increase in value.

The standard method for controlling the gain is to put a resistor in series with the emitter capacitor. Then the AC signal will see a resistor as well as a capacitor at the emitter.