Question about increasing model accuracy

Hello, I am working on a project to detect and classify different types and stages of brain cancer. My issue is that no matter what I do I can’t get past ~80% accuracy. I have looked into various resources and papers and I can’t notice anything else I can do other than changing my model to a Dictionary Learning Model (I am currently using a CNN because I am quite new to machine learning).

If anyone could help me out if I have any obvious code errors or if they have any ideas on how to improve the accuracy that would be great.

Here is my code