Pre-trained CNN model makes Poor Predictions on Test Images Dataset
Kaggle's Dataset is really noisy and it is really tough to get very good result with simple models. You have to do lots of preproccesing ,Data Augmentations and larger network for many more epoch to get a good result.
Things you can do :

Go to notebook section of your competetion and look out for some preprocessing and augmentations and apply them.
Use some regularizer like dropout, mixup,cutmix and many more.

3.Train your model for more epoch

Train a larger model.