Hi
Firstly ensure that your preperation is spot on.
Make sure that no product has touched the skin surrounding the nail
MAke sure your application is perfect, ensuring your ratio is correct and your product application is coorect.
Finaly the finishing, you should be shaping with your brush and not your file, mak sure they are no ridges and that the product is not too thick arround the cuticle area.
Hope this Helps