Since you mention it is a imbalanced dataset, I would not focus on accuracy but other form of loss and metrics.
During training,

There is WeightedRandomSampler which you can use (please search in this forum and you will find answered queries). Or,
You are using CrossEntropy loss. This accepts weights for each class. Look here 36.

For metrics, you could look at F1 score
You can explore the above and see what works. Let us know.