I had a similar experience with my 2017 350CBR with inaccurate fuel reads.
In fact, from day one, I could never get a reading that I trusted; Formula replaced the tank sending unit under warranty, but that didn't fix the problem.
I was never able to solve the problem during my ownership, but here's how I managed it:
1) Set the analog dash gauge to display whatever the sending unit was telling it.
2) Configured a display on the VesselView to show fuel remaining based on quantity in the tank minus fuel burned.
3) For #2, each time I'd add fuel, I'd enter the quantity into the VV.
This way, I had two measurements at any given time, and I could compare them.
(Not going to lie, this was highly frustrating, especially coming from a boat that was pretty spot on in its fuel level accuracy (a 2011 SR).)