Hi, I have the earlier Ecosport 2016 and steering is light and fine, and does not need any correction on the straight, but cannot talk about the newer facelift Ecosport 2017 onwards as have not driven it yet and it has a different design of steering.
Likely someone will confirm if there is any excessive feedback of the electric motor steering which is programmed to the movement of the steering shaft, ie, having to correct on the straight, which does not seem right.
The only reason for correction on the straight, is if the road has a camber (angle), but this is not constant correcting.
A few years back I had a Ford company car that worked on a hydraulic pump system and it had bad feedback needing constant correction to the steering wheel, I took it back, and they adjusted something to make it have less sensitive feedback, an it was then OK.
What i would do...
see what others say on here about 2018 steering.
and I would go back to Ford and ask to try driving a different ecosport and see if it is doing the same thing, ie, needing small movement corrections on the straight. If not then your car is at fault. It definitely does not sound correct to me, and needs the feedback adjusted to be less sensitive.