Hey,
Try to check with two classes and also upload 100 images per class and see how is the accuracy then add the third class images and check it out. As long as for three classes 100 images per class will be enough.
Coming back to this issue, I am still seeing very odd classifications on images and wonder where the problem is.
If you look at the attached image, you will see that the image is of an elephant but the prediction is chimpanzee.