ibelova, if you don't understand how taxes work any better than this, do yourself a favor and get a tax preparer to do them. You haven't got a clue how self-employed taxes work.
Or are you filing as a hobbyist? If you are, and you were worried about a parking expense, I guess you're not deducting your mileage either. Which means you're paying taxes on the $575 or whatever that you probably don't have to.
Or were you not going to put your mystery shopping income on your tax return at all?
Get a tax preparer.
Time to build a bigger bridge.