How can I normalize my output data for neural network?
Normally, you shouldn't make normalization on your target data. If you want to increase your accuracy of model, you can try different neural network architectures or activation functions and monitor your train/val/test scores.

If you insist to normalize target data, then you may want to convert your predictions and then calculate the accuracy.

Steps may be like below:

normalize data =&gt; fit model =&gt; take predictions =&gt; denormalize predictions =&gt; calculate accuracy