Eating after suhoor time by mistake

I oversleept and missed the suhoor time, but thought that my mother told me its 2:45 my brain took it that way and got up just ate something small then my nonfasting brother this day because he was sick last day told me its in fact 3:45 and suhoor has 15 mins that it has ended and i didnt know what to do i am keeping the fast, is the fast valid ?