Welcome to Healthcaremagic,
As per the description provided by you, the white oval spot is suggestive of an apthous ulcer. It is mainly due to trauma from sharp cusps that injure the tissue of your cheek while biting.
You can wait for a few days and it should disappear by itself. In the meantime you can apply Hexigel on the spot twice or thrice daily.
If the spot doesn't heal up in a week, I suggest you see a local dentist
who will evaluate the spot and may ask you to get a biopsy
done to ascertain a diagnosis.
Hope this helps.