There are many ways to prevent overfitting, I will list some of them:
1. Dropout: remember that you can use dropout between ConvLayer too, maybe value ~0.2
2. BatchNorm: it reduce overfitting too
3. Data Augumentation: add rotation, cropping, mirror, color manipulation
4. Decrease power of model: get smaller number of parameters. By removing a layers or replacing FC layer by ConvNet
5. Model Ensemble: training several model and getting average of output always decrease validation error.