Not to worry, you are good.
The fan on a psu is for intake.
If the psu fan needs to run at all, it sends heat out the back.
The value of a 135mm fan on a psu is that it can run slower and quieter.
Most good power supplies are so efficient that the fan never needs to run at all.
The opening on the bottom of your case is plenty adequate for whatever the psu might need.
As you can see, the bottom legs are tall enought o allow airflow under the case.
Do not put the case on a carpet or such that could restrict the airflow.
It looks to me like there may be a filter that can be fitted to the fan area to keep dust out of the psu. Installing one would be a good idea.