First, when the heat comes on at an inappropriate time, does your Nest's (or app's) screen show that it is calling for heat because it believes that its target temperature is higher than the room temperature?
Second, have you programmed a schedule, or are you trying to operate the Nest manually only?
Even if you never set up a schedule in your Nest (because you want to operate it strictly manually), there is probably a default schedule in there. When you twirl the dial or click buttons in the app, that's only a temporary command; the Nest will revert to its schedule at the time of the next set point.
Nest thermostats are designed to run on a schedule but if that's not what you want, you can delete the schedule. Click on Schedule to edit the times and temperatures to your liking. If you don't want a schedule at all, you can perform a reset that wipes it out. Follow the instructions in this article: https://support.google.com/googlenest/answer/9247296?hl=en&co=GENIE.Platform%3DAndroid#zippy=%2Crese...
(I'm sorry if a lot of this misses the point; I couldn't tell from your post exactly how you're trying to control the Nest.)
