Got a breakfast taco at a food trailer this morning, Now I have guilt that I don’t deserve

Was starving for breakfast so I pull a U-turn when I see a taco trailer with an open sign. Order a bacon egg and cheese taco, get told it’s 3.50 So I hand the lady at crisp new $20 bill, 3 new $20’s are all I have on me. She takes a minute at the cash register and hands me $1.50. I am immediately state that I gave her a $20 bill. She looks at the register and pulls out a crumpled five dollar bill and shows it to me and says “are you sure you didn’t give me this ?” I tell her no, all I had was $20 bills. At this point she turns to her husband and says something quietly about being certain that I gave her a 5. At first I thought she was trying to rip me off, but the look on her face and the tone of her voice made it evident that she thought it was I that was trying to steal from them.

She gave me my taco and correct change. But now I’m driving down the road Feeling bad, these people obviously need $20 Way more than me. I wish I would’ve tipped the change, all of it. She was sincere, but wrong, but I hate the thought of good hard-working people thinking that I stole from them and I would’ve rather given them the money. And I have a breakfast taco beside me in my car that I’m frankly nervous about eating .....