Hi ladybug and welcome to the Chiari forum.
Not being a medical professional....I can not say you do or do not have Chiari or a related condition/issue ....you will want to have a Chiari specialist review your MRIs......and from different angles and slices....
Again since I am not a medical professional....I am not sure but it is possible that you may have a retroflexed odontoid ....
Chiari is the malformation of the skull and I am not sure how to identify that....I can tell if there is a herniation of the cerebral tonsils which for you do not seem like they are herniated, BUT may be tight causing some issues.
Have you had a CINE MRI? Other testing...MRI of the complete spine?