My csection was 2.5 years ago now, but I remember it was quite bumpy to start with. But I used Avene Cicalfalte cream (reference link below) religiously for many months after (it was recommended to me by the nurses) and now my scar is almost invisible and definitely lump & bump free.
I think the massaging-motion of applying a healing cream helps reduce the bumps.
Perhaps yours will smooth-out if you do the same. Goodluck!