How worried should I be about my performance?

I don't think you should have any guilt regarding "I'm getting paid more now, therefore I should work more hours".

Getting Things Done on Time

That being said, your projects need to get (mostly) done on time. Maybe you could discuss with your manager why your projects are running behind. A couple common issues are:

1. Scope creep. A 3-day issue turned into a 7-day issue because you or someone else added to it. Fix: Make a follow-up ticket/diff for the new additions.
2. Getting rug-pulled. The team agreed to the scope of a ticket/project but they say they wanted way more features at the finish line. Fix: Get people to agree to written requirements before implementation.
3. Code review takes too long. Your code is too annoying to review, so nobody does it. Fix: Alex discusses splitting diffs in the Level Up Your Code Quality course

Don't be afraid to call people out on (1) and (2), as it's now your reputation on the line.

Gracefully Handling Lateness

Regarding being late for projects, things always come up in a startup. By default, some projects are going to be late. It's how you handle the lateness I think, that really matters. Some key things to ask yourself are:

• Are you communicating with the team that solving issue A will delay project B by # days? How well is news like this received?
• Is your dev pace matching/exceeding current members of the team?
• Who is doing your performance review?

Performance Shouldn't Be a Surprise

Finally, your performance review is basically at the mercy of whoever is in charge of that. I think that given you're not even 90 days in, it's impossible to give a definitive or close-to-precise answer. If someone got let go in 90 days, that means they legitimately did nothing, so I wouldn't worry too much about that. (if that's only a single data point)

To answer your question, there is never a guarantee that your team will let you know that you're underperforming. If I were in your shoes, I'd bring up your concerns with your manager (who I'm guessing will do your performance review) and see where you guys can iron things out. If possible, it's good to gather your thoughts and do this asap.

Talk to your manager. Ask them to be brutally honest with you (if necessary), and that you're open to any and all feedback. This feels scary and awkward, but that's the entire point of an effective 1 on 1 meeting.

Don't leave things to chance. It seems like you have a good thing going here, so it would really suck to lose this job. You need your manager to tell you point blank whether you are meeting expectations or missing them in a meaningful way.

Startups are supposed to hire and fire quickly, and the holidays are also coming up. I would try to have this conversation with your manager either this week or the next. You can even let them know before your next 1 on 1 that you want to have an honest conversation about your performance, so they can "pre-compute" and holistically go through your accomplishments before the meeting. Sometimes managers don't even know that one of their reports is a low performer until they crunch the data - I sadly saw this happen a couple of times to others back at Meta.

On a side note, you generally are expected to work harder at a startup, think 40-50 hour weeks. It comes with the territory. So I'm not surprised that you're falling behind. To help out, I highly recommend this: [Course] Maximize Your Productivity As A Software Engineer

I am wondering for now would companies generally give me a notice in advance if I am underperforming?

This has less to do with the company and more to do with your manager.

And in particular, this has to do with your relationship with your manager:

• How often do you talk?
• How often do you receive feedback from your manager?
• Does your manager seem invested in your success?
• How plugged in is your manager? (if your manager is incompetent and on the way out, their opinion doesn't matter much)