How does my piston look
 

I just took my pipe off and look through the exhaust port. I see some vertical lines. Not sure if this is normal or not? I have not work on 2 stroke bike before.
About 50 hours on 2018 XC 300

What am I looking at?

The pistons come with a coating on them. It tends to wear down. The piston moves up and down, so any wear patterns will usually be like that. A gouge such will be more than visible.. You'll feel it.

Most people inspecting piston wear through the exhaust port will be checking skirt wear (bottom front face of piston) which will polish up and allow the piston to rock a bit.. Ring wear, which shows as carbon passing below the rings; aka blow by.. and the cylinder wear on the far side of the jug at bdc.

You should also have a nice coating of oil on the piston as you cycle it..

From what I can see, it looks good. :)

Very small image, but seems to look good.