Freelancer between 3 states

I am an Oklahoma resident that occasionally traveled to Kansas City for work at a job based out of California.

What kind of tax rates should I be expecting?
Turbo Tax placed my blended tax rate at 45%!

The total income earned was under $20,000

The employer lives in Missouri currently and is "Doing Business As" out of California.

 

https://www.kiplinger.com/taxes/tax-brackets/602222/income-tax-brackets

shows a tax rate of 12% for taxable income between $9,951 to $40,525

 

Question 1: A blended tax rate of 45% is outlandish, how can I verify this is correct?

Question 2: Must I file a California state return even though zero dollars were earned physically in the state? ( I never traveled or spent time in California)