Thanks for the pics- if you can I'd love to see the back as well.
This looks like a Y-seam problem and stretching problem.
Even if the block is stretched, that extra fullness should be worked in within the 2 stopping points.
The Y-seams on the individual block look like they are done well, and are laying flat.
Are you marking your stopping point? Do you sew from the edge in to the Yseam or start at the Y and sew your way out?
So hard to ask questions - it's such a visual thing.
I'd love to see a pic of the back, along with a close-up of one of the joins that are bunched-up.