I'm sorry you're dealing with this. First off, you did what you thought was best. If the cyst was truly a dermoid, it would not have resolved on its own like a lot of other cysts do. So surgery would have been necessary. Also, it's better to have part of an ovary versus none of it. Even if the part containing the eggs was removed, I believe you would still be left with its non-reproductive / endocrine functions which are important for many aspects of health long after menopause.
As far as fertility - Of course, having both ovaries gives one the best chance of conceiving. However, it's possible to conceive with just a partial ovary. So hopefully, you'll be fine with one ovary plus a partial one. At least you know upfront that your chances are somewhat reduced so you can make allowances for that (e.g. begin trying earlier, seek fertility help sooner, etc.). An earlier menopause is a possibility. If it's quite a bit earlier, you may want to consider hormone therapy for bone health, etc.
I wish you the best.