Hello flight simmers.

I am having a problem with the heading hold mode and LNAV. When I select the desired heading, and pressing the heading button, it doesn't turn to the desired heading. As soon as I try turning it a little bit manually, it right away corrects to the original heading, which is usually the runway heading of the runway I start on. After that, I switch to LNAV and the aircraft does not follow the flight plan. Is this something to do with the "HEADING HOLD"? How can I switch it so it follows my desired heading?

Any help would be greatly appreciated as always. Thank you and safe flying!