As a native English speaker, I mostly agree. To "prepare yourself" does not necessarily imply bad things coming, but generally something that could be stressful or overwhelming. For an example of a potentially good thing, you might need to prepare yourself to go on a first date with someone you really like. But definitely it's at least for something that is going to be stressful in some way. It is about working on your mental composure.
Swedish 'förbereder' is more prepare for a date kind of thing, or a party or a family dinner, with a lot of cakes to bake, food, and other preparations. But of course the context could also be some kind of stressful event, at least someting that needs preparations, e.g. a trip, a course. ... But, I prepare myself for what may come = Jag är beredd på vad än som kan hända. .
I would say that förbereder is the more common, appropriate for all kinds of 'preparing'. But for a more stressful situation, I would change it into vara beredd, here I have already done all the preparations, I 'am prepared for what may come', Jag är beredd på vad än som kan hända
I answered correctly, but I wonder, would "I prepare for the weekend" be accepted? As rwhodges said, in English to prepare oneself implies an expectation of a challenge or stress of some sort. I would guess that the Swedish sentence above has the meaning of getting ready for the weekend.
I think it should be accepted if it isn't. I believe Förbereder is a transitive verb and needs an object, but prepare can be intransitive, so myself is not needed. Including myself makes it seem a little more intense than I believe förbereder to be in Swedish.