I will not comment on the blister-like growths to which you refer in your last addendum because they are not evident in your photograph. They will be easier to identify if you present to your dentist for evaluation when the lesions are manifest. (As an aside, the three most common reasons for intraoral blistering are mucous retention cysts
, viral infections
, and vesiculobullous autoimmune disorders, in that order. None of these three are malignant.)
The structure evident in your photograph is not the parotid gland per se, but rather the orifice of that gland's duct (Stenson's duct). Although your photograph lacks the resolution required to render fine surface detail, the tissues look grossly normal. Quite naturally, the oral mucous membranes are vulnerable to mechanical injury and irritation, and may vary in appearance from time to time according to normal functional (e.g., chewing) or para-functional (factitial injury from habitual cheek chewing or manipulation by the finger) trauma. Although there is a general pattern of symmetry within the mouth, it is never absolute, and the left and right Stenson's ducts need not mirror each others' appearances in order to be considered normal. Based on your photograph, I am inclined to dismiss any suspicion of abnormality here, other than the referenced canker sore.
As for the canker sore, I would discourage the use of hydrogen peroxide, which can be irritating. Over the counter topical anesthetic products are helpful in mitigating symptoms, but there is little that will hasten the natural healing process. If you experience repeated crops of severe canker sores, you may wish to present to your primary care medical doctor to rule out certain systemic issues (e.g., Crohn's disease, Behcet's syndrome, lupus, Reiter's disease), as recurrent multiple canker sores (aphthous stomatitis) may be related to a more global disorder.
Hope this helps...