Nacho cheese is okay to eat when pregnant.
Just be sure to heat the nacho cheese up hot enough to kill any Listeria that may be in the nacho cheese.
The reason that nacho cheese can be bad to eat when pregnant is because of the bacteria which is Listeria that can cause harm to the unborn baby.
But as long as you heat the nacho cheese up hot enough the Listeria is killed off and there's no risk of Listeria.
I've eaten Nacho Cheese that I made at home when pregnant and my babies were born healthy and the pregnancies went just fine.