Hello Chiang,
Here are some of the pointers I learnt through MLS course. Probably it might help you
In the below image 
, baseline performance depends on the analysis and it can be human level performance, or performance of other well-established models, if your model’s training error is much higher, then this is a sign that the model has high bias (has underfit).
Hope now you have a better understanding. So probably because your batch size is shallow, check into additional features and reduce your learning rate.
Regards
DP