First, essentials oils are super powerful and need absolutely to be HIGLY diluted in a carrier oil. They can't be mixed with a serum or watery cream cause essentials oils can only be diluted in oils. I also higly recommend to not put essential oil on your face in the morning to avoid burns or any kind of reaction due to the sun.
Not to mention to always to a patch test.
Now, among essentials oils tea tree oil is really harsh and it can burn the skin easily. Why did you put in such a large part of your cheeks ? You don't seem to have acne.

I had similar burning patches with exactly with the same color when I burnt my leg with boiled water. It took almost one year to came back to a color near my skin color (it still is somewhat different)

Some advices that will help you I hope :
-always put sunscreen on your face everyday. the sun will make your burn darker by activating the melanin.
-be super gentle with your skin - stop any essentials oil or cream with actives
-keep your skin hydrated and moisturized at all cost - use a healing oitment at night like aquaphor or vaseline (they are non comedogenic)
-you can use carrier oil like tamanu oil to regulate the pigmentation and heal the skin. I love also unrefined shea butter. High quality unrefined shea butter doesn't clog pores (I have combination skin with a super oily T-zone and it never broke me out)
But first, the most important I think is to use aquaphor or vaseline (after you put an hydrating cream and moiturizer)

Sorry english is not my native language.
I hope it can help. Good luck

I think you should seek a help from a doctor for immediate remedy. Though what Kixhikari said is true.

How long did you take to heal??

Hi did the scar peel off please reply I had a similar situation and I'm too worried

Hello did it heal?

@s_kalkeri hello, did yours heal