Error using trainNetwork...output size (4) of last layer does not match the number of classes (2)

I have downloaded example code from this MathWorks tutorial to try my hand at training a neural network from scratch: https://www.mathworks.com/videos/training-a-neural-network-from-scratch-with-matlab-1492008542195.html

The tutorial states I may replace the training data in the example code with my own and that is what I have been trying to do.

The error in my code occurs at the line:

[net, info] = trainNetwork(imds, layers, opts);

The error states:

Error using trainNetwork (line 170)
Invalid training data. The output size (4) of the last layer does not match the number of classes (2).

I suspect the trouble lies in the code that I am using to load the training data, as I am unsure of whether this code loads the images as necessary:

categories = {'dogs','cats'};
rootFolder = 'C:\Users\js\Desktop\training'

imds = imageDatastore(fullfile(rootFolder, categories), ...
    'LabelSource', 'foldernames', 'IncludeSubfolders',true, 'FileExtensions','.jpg');

I am trying to load training images from two folders containing 32x32 .jpg images of cats and dogs: ...\training\cats and ...\training\dogs

Are the images being loaded properly and is that the source of the error in my code?

Thanks!