I got kicked from a party because I was doing too much DPS healer this week.
No matter what you do, someone in this game think you shouldn't play as you do and will be needlessly aggressive about it no matter how you perform.
And better than doing because you should do it, do it because that's how you want to play. If you're interested about more difficult content about the game, you must be interested in playing your job in a more optimised way. DPS is just a part of that, not really something to be concerned with that much.

That said, it's a sane approach to be concerned by your performance, especially as a healer. I'm not sure how this sound like, but it's more because having a sense a responsability is a good thing while a lot of player in this game go for "everything is easy". If you're stressed about it, it means it's not easy and it won't get easier when you're more confident about.

You shouldn't be stressed about playing a video game, but you should keep in mind what you where concerned at that time. It'll later show you how much you progressed and where you'll likely to make mistakes no matter you much you progressed.
Mistakes doesn't really matter in a video game anyway, enjoying the learning process is much better than being stressed over it.