I know that there's a huge demand for software engineers, and just about everyone can think of the time their company inexplicably hired someone who couldn't do FizzBuzz. But if you've already been hired as an engineer and you've worked there for 1.3 years, at a level comfortable enough where you actually want to keep being an engineer and move on to a "better" company, and you're willing to put in 10-20 hours extra a week studying, then you aren't not cut out to be an engineer. You clearly have the mindset and tolerance of rigor that the job requires.

But it's possible that you aren't cut out for whatever benchmark/ideal you have in mind for software engineering. If a company is looking for the next Jeff Dean, sure, being not confident in algorithms is going to put you at a severe disadvantage. But there are plenty of valuable and important software engineering jobs -- even within the domain of just programming, nevermind design, planning, management, etc -- that aren't limited to those who can show a mastery of algorithms.

One well-known contemporary example: https://news.ycombinator.com/item?id=9695102

My main job is not software engineering right now, though I do a lot of it on my own (to be better at my actual job). I think I'm similar to you in that I was probably mediocre in comparison to the best of the class, though unlike you, I was probably in self-denial of how mediocre I was. But I eventually got into it much more after working in non-software jobs and understanding how the world works, and that there's plenty of uses for programming beyond the narrow scope of what's taught in CS curriculum. It's equivalent to thinking that you're not cut out to be a writer after feeling mediocre in a journalism news writing class, or technical writing, or poetry.