Blur and glow effects

In general, I did the animation of the shape, and now I need to add this effect as in the video https://youtu.be/XWw6sxAQYDY?feature=shared , I tried to add blur and glow, but they went beyond the boundaries of shape 1 (I created two shapes: shape 1 and shape 2, shape 1 is the main animation and shape 2 is trail, and blur and glow 2 trail shapes went beyond the boundaries of 1 shape). Can you tell me how to make sure that they do not go beyond the borders? 

Thank you!