You're talking about 2017 taxes? Relax, they're not due until April, so you're not going to get hit with a fee or penalty or even interest, as long as you correct the mistake (by April 15). In general, you almost never get hit with fees or penalties (providing the return was filed in good faith, and not intentionally fraudulent - which seems to be the case here). However, you will probably be required to pay interest on any amount that you owed, but did not pay by April 15. So if you correct this by then, you won't even owe interest.
Also, for future reference, if you're required to fill out a tax form, then ALL income needs to be reported, regardless of how much or how little, whether you got a 1099/W2 for it, etc.
Disclaimer: I'm not a tax lawyer, so don't take tax advice from me!