Kaggle Sentiment Analysis Movie Reviews

I’ve created a Kaggle kernel based on documentation at https://docs.fast.ai/text.html my Kaggle kernel is working but the results are not so good. The best public kernel has a score of 0.706 and my best score was 0.517

https://www.kaggle.com/dromosys/fast-ai-movie-review/

Any idea’s on how to improve it?