Canvas texture feedback loop transparency edge problems

Hi together,
I’m trying to create trails of a canvas2d in a webgl texture using a feedback system. I always get edges on the canvas2d shape, I don’t know how to get rid of them. Somehow there seems to be problem with the canvas2d transparency, I’ve been looking into custom blending, premultiplied alpha and so on but no luck.
If anybody has an idea, I would really appreciate it.

Thank you!