LT8316 Voltage Spikes

Hello everyone,

I am facing a problem and I hope someone can help me with.

I am student Electrical Engineer, I am trying to build a flyback converter which converts 350 V DC to 12 V DC at 0.125A.

I used the demo circuit made by Analog, see circuit below.

I have built a PCB with the recommended components written in the datasheet of the LT8316.

The design works, I do get 12 V DC output, but the 12 V signal has a lot of voltage spikes of about 2V peak-peak (yellow line). See picture below.

The signal on the drain of the MOSFET looks like this:

See below me PCB design:

I followed the democircruit, what did I do wrong?

Image of the signal on the drain of the MOSFET.
[edited by: Flyback converter at 1:09 PM (GMT 0) on 22 Dec 2019]