There are a number of things you could do you can take chicks at day old from both hens and reset both of them that would be the only way you would need a heat lamp. Or take one hen seperate her from the chicks and she will stop being broody or you can seperate one hen and her chicks and reset...
My incubator did the same thing i had to reset the tempature two time a day morning evening youll have to keep an eye on it as long as it doesent stay at this temp for long periods of time you should still get some to hatch