So, if you are trying to add post processing effects, you generally shouldn’t do it with canvas/rects. You should be using render passes to apply the effects, especially if you want to apply multiple effects at the same time.
And I’m a little confused about your rect issue because it looks like you’re just using the camera texture. In that case you could just set the rect to 100% relative size and then you don’t need to do anything with the scale. The texture will fit exactly on the screen.
If you do need to use rects, then I would suggest resetting the position and size values.
This is what I’ve been trying to do, but the dimensions still doesn’t fit (Thank you for your help really and sorry still too new to the whole process)
Just to mention that this is the same filter I used for the first Click of a polaroid filter
Sorry, I’m still not clear about what you are trying to do. Do you just want a smaller rectangle in the center of the screen? I don’t understand what dimensions are wrong in that shot.
The small rectangle currently in the centre of the screen I want it to fill the whole screen’s filter without stretching
You can set scale to 1 and use 100 relative width and height. That will fill the screen.