Please do not hesitate to inform your parents if you get injured. Getting hit with a ball does not mean that the injury is mild or can be left alone. A person can receive a serious injury with any moving object and it not necessarily have to be something hard as a metal or a fall on the ground.
Discuss your symptoms very clearly with your parents and keep them informed.
is a minor head injury
that can result in loss of consciousness
A mark on the cheek is just an external injury that you have mentioned. There could have been an internal injury as well. If you are unable to stay alert or awake, feel dizzy, or develop vomiting
episodes, it certainly needs a medical evaluation. Do not think you will sound silly if you discuss with anyone.