You probably have a 'serious' defauit look that a lot of people consider intense and read as angry. I had to practice seeming warmer and welcoming when meeting people for the first time by being aware of how I feel and trying to think of how friendly I would want someone to be and emulating that. Like getting practice at public speaking it seems to have worked out pretty well.

Looks do have an impact, but a lot less than the vibe one gives off. If you have internalized looks as being so important it can lead to giving off a resentful vibe.