After you shut the engine off it's best to wait at least 5 minutes for the oil to return to the engine oil pan.
If you check the oil too soon then you can get a non accurate oil level reading.
Also make sure the vehicle is on a level surface when checking the engine oil because when the engine is not level the oil level can read wrong.
Pull the dipstick out and then wipe it off and then put the dipstick back in and pull it out a second time to check the oil level.
After 5 minutes of the engine sitting the oil level reading should be accurate.
I usually check my oil after pumping gasoline because by the time I pump the gasoline into my vehicle the engine oil had enough time to go back to the oil pan.
I always check my oil level every time I get gas because I want to make sure my engine has enough oil.