I am using package marginaleffects in R to get confidence intervals for my predictions of a marginal effect. However, I did some calculations by hand and some of the confidence intervals I am getting with marginaleffects::predictions seem too large. Am I missing something on how these confidence intervals are calculated or is there something weird going on?

I have the following regression model: Y = b_1 endogenous + b_2 endogenous^2 + b_3 controls + error

Because I have endogenous variables, I employ instrument. In terms of code, I use package fixest to estimate the model below:

model <- feols(outcome ~ control1 + control2 + control3 + control4 |
                    fixed_effect1 + fixed_effect2 |
                    endogenous + I(endogenous^2) ~ instrument + I(instrument^2) ,
                  data = dataset,  se = "cluster", cluster = "cluster_id")