Do not overthink things, you'll go crazy lol.
If your most recent tax return didn't meet the required income, then you can use bank statements to prove that money is getting deposited into your bank account,
paystub, etc. and maybe a letter from your employer to prove that you are a permanent worker that is earning X amount of dollars.
At the end of the day, they will only want to know if you can financially support your fiancé and not rely on the government.