Hi,
Transformer power output (Pad6, 7):
This is called "ringing". It should be suppressed by R7, C7.
R7 needs to be a high frequency, low impedance resistor. No wire wound!
Spikes:
All your elecrolytic capacitors are not good to suppress HF switching noise. I recommend to add parallel ceramics capacitors (foil for primary side).
I`m no friend of single sided PCBs, expecially for switching power circuits. GND wiring becomes critical.
TOP_PIN4 is power GND, therefore use thick and short wire to C2.
TOP_PIN5 is signal GND, therefore route it separately to C2, width is not that critical.
Safety:
* I doubt that optocoupler wiring is according (european) safety regulations. Check creepage distance, clearance.
* C6 needs to be safety approved "Y" capacitor.
Klaus