Can profs from your first semester still make changes to your first semester course grade if there is any outstanding issue or work?

For example my prof put my final grade as "Inc-Incomplete" and he said he would change it later but I think he forgot. I should have reminded him.

Yes, grades are not final until you get your final grade report in May - and even then, grades can be changed, but the prof has to jump through a few more hoops.