A very generic guideline that is often used is to have three arguments/aspects/... This is often structured in the form of a Five-Paragraph-Essay where you have one paragraph that you use to introduce the general topic of the essay, then three different paragraphs exploring each argument/aspect/position/... and then one concluding paragraph.
You might have heard something similar to the following for the content of the three different parts of the essay:
First you tell your reader what you will talk about. Then you talk about it. Then you tell your reader what you have just talked about.
The problem with this is that such an extreme simplification tends to trivialize the process of creating a meaningful essay. I prefer the approach:
It's not perfect when you can't add anything - it's perfect when you can't remove anything.
While the introduction - content - conclusion structure itself is useful the length of each section should be as long as it needs to be to convey what you are trying to tell your reader. If those two points you already have are enough to tell your reader what he needs to know, then there is little need to add a third point. In fact, it would make your essay worse as you have to probably take away some parts from the two relevant points just to add a third point that you didn't consider to be relevant until now. As a reader I'd much rather read two useful points that the author is talking about in the appropriate length than three arguments where one feels a little off and all of them feel like they are too short. The content doesn't need to be arranged in the form of paragraphs, too. Just in the form distinct parts, no matter how many paragraphs each part consists of.
But ultimately this is not something that we can answer with certainty - it depends on your assignment/framework. If someone tells you to have at most 3.000 words then you ought to have at most 3.000 words (+/- 10% were usual for me, but this is up to the person giving you the task). If the requirements are that you ought to have three arguments than you need three arguments.
If you are free to choose the amount of aspects you can cover in your essay I'd say that you should stick to the two you have and put your energy into making them as good as possible instead of crippling them in favour of a third one that you have to find first.