How do I handle with my Keras CNN overfitting
as your data is very less, you should go for transfer learning as @muneeb already suggested, because that will already come with most learned parameters and then you can train that model using your custom dataset.

you can try out pre-trained models from here

If you want to go for your existing custom configured model only, try adding another Dense layer before the output.

like a Dense(128, activation='relu').

Share your results here, so that we can explore more.