It always works that way. How do you control brooding heat with a heating pad?
Or allow cool spots for chicks to move to when they need it?
Normally the brooder bulb burns out just when you need it too.
Your ideal is 37.5c so you are not that far out. If it is a still air incubator(no fan) your temperature is just about perfect. Either way I would leave it alone.
Time to increase your humidity and stop turning eggs. This close to hatch temperatures will spike in a small incubator. That is...