[50656E6973]

>Act only in accordance with that maxim through which you can at the same time will that it become a universal law.

That seems entirely too tyrannical, imperialistic, and egotistical to be practical.

Where does having freedom, humility, and an open mind fit into that maxim? I.e. being willing to accept that all humans (including ourselves) can be misguided, or that someone else could know what is better for them than me?

[Retra]

If all humans can be misguided, any principle which accounts for it will be universal. If someone else could know better than you, you can also account for that in a way that other people could be equally well served by.

So there isn't anything contradictory or inhibitory there. Perhaps you are not seeing the generality implied by the term "universal?" The contrapositive here is to not act in a way that assumes other people are incapable of, unworthy of, or disadvantaged by following your example. There is nothing here that implies one can't be humble or liberal. To put it in less gentle terms, the point is that if you don't intend for other people to emulate you, then there is no point to your life in human society.