Flat red spot on my face looks like a reddish skin patch what could it be?

Examination! From the description it's very difficult to give a differential diagnosis. I recommend you going to your doctor to evaluate and determine proper treatment plan.
Almost anything. It could be an allergic reaction to something that touched your skin, or an irritant (non-allergic) reaction, or a fungal infection (ringworm), or any number of other things. A dermatologist needs to see it in person to narrow down the possibilities.

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Flat red spot on my face looks like a reddish skin patch, what could it be?

Needs to be seen. This could be a precancer (actinic keratosis), a full blown skin cancer, eczema, a boil, or many other possibilities. It should be evaluated by a healthcare professional if lasting more than a week. Read more...