hey @ptrblck - I had corrected my mistake earlier by adding the pre-trained model to a Sequential module with the final FCL.
nn.Sequential(Resnet50, nn.Linear(1000, 3))

This worked great. What I was confused about though was, why/how would a model with 1000 outputs successfully train on a dataset with the labels?, being that before recognizing the mistake, the model had trained for 50 epochs on 2000 images and was correctly classifying at 68% accuracy.