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Thanks for the picture.
It is not likely cancerous. And it does not look like most typical cancerous lesions, which are white-ish with irregular borders and not smooth. But, to be safe, it should be evaluated to rule out anything serious, such as Blue Nevus, which presents as blue discoloration on the palate and can sometimes be cancerous. Your dentist will be better able to examine this in detail tomorrow. Waiting is difficult but try not to be overly anxious. It is most likely harmless.
Let me know if you need additional information. Otherwise a positive rating would be much appreciated.