Your attempt at translation is pretty much spot on in terms of meaning; I think all you're missing is an understanding of
のではない, which is more commonly seen as
んじゃない and is used to make statements into rhetorical/tag questions confirming something the speaker believes is likely true. You can read about this here and here, and in many questions on this site including this one and this one. The important thing to realize is that
んじゃないか is just a contraction of
のではないか. In this case it's also inside a subordinate clause describing what the speaker is worried about, making it slightly less direct.
Given that, the sentence works out something like this:
Won't it turn out the same way this time?
I'm worried that it will turn out the same way this time.
If you have trouble with the idea that
won't it turn out the same way? stops being a question of any kind in the full English translation, you can also think of an extremely direct translation along the lines of :
I'm worried thinking "won't it turn out the same way this time?"