You need a larger value for C2.
When you are taking 300 mA, C2 has to provide the current for just under half a mains cycle.
The charge is 0.3 * 1/120 = 0.0025 coulombs. The voltage drop for a 220 uF capacitor would be
0.0025/0.00022 = 11 V,
That is not a very accurate calculation, as the time will be a bit less than 1/2 cycle, and the value of the capacitor has a large tolerance on it, and the current might well be less.
You should aim for about 2 V drop each half cycle, so you need around 1000 uF or more.