I'm confused about this scenario. Reading between the lines, it sounds like you were put solo on a project with very little guidance, just as you walked in the

I'm confused about this scenario. Reading between the lines, it sounds like you were put solo on a project with very little guidance, just as you walked in the door on your first job. No team, no mentor, no buddy, no code reviews, no daily stand up, no issue tracking (which is a way of measuring progress). This sounds like a place that has not upgraded its software development practices in years, if they even know what they're doing at all. The first feedback you get is from boss's boss, who directly criticized architecture, coding decisions, and timeline? No. This is not on you. Here are lots of replies telling you to be a better communicator, which is always good, general advice, but this is not a good situation, and will not teach you how to be a better software engineer. "Do better" is just terrible feedback. I know that you like this job, but know that there are better places out there, and that better places would never strand you like that.