It seems like the nozzle for my pretreat machine is spraying more on the right side than the left. I think it's clogged with the pretreat.

Nozzle do wear out every 2~6 Month depending on the volume

When you are done with pretreat, you should always take the nozzle out and soak it in our cleaning solution:

Purge the line daily with water and purge the line every week with cleaning solution

It could be the filter on the hose, make sure it's not clogged up.

It can be the check valve: