Filing taxes with part time prevailing Wage

Hello, I work a job where I will sometimes work about 4-8 hours of prevailing wage work per paycheck. My company gives me a separate pay check with these hours worked alongside my regular paycheck.

 

Is this normal? I end up owing around $800 State (CA) and usually about $50 federal every year, so I have recently started adding $50 to every paycheck to not having to pay a lump sum at tax time.

 

I am a Renter and file the standard deduction.

 

Please let me know if there are any questions I can answer to help out with the question.