Do NOT ask for someone else to take over.
That's pretty much the worst thing you can do.
Of course everyone needs some help occasionally, but simply giving up on the entire project would be an extreme option.
You've already spent months on it, so any new person will probably take quite a while to get up to speed (quite possibly longer than you'd take to finish it). This is also assuming there's even someone at the company with the capacity and knowledge to take over - otherwise you can add a few weeks to months of going through the hiring process to this as well, for someone the company might not need beyond this project (or at least they might not need both of you).
A good manager will probably just give you a pep talk to motivate you. And that will be all that happens, or they might suggest some other solution (which may some guidance), if required.
A bad manager will lose a lot of confidence in you and might just say "ok" and you'll find yourself looking for another job.
Overall, you don't have much to gain by saying this.
What you can do is:
Discuss the state of the project with your manager.
You need to ask them:
- How they think the project is going
- What they think of your performance so far
If they say everything is good, you shouldn't worry.
If they express some concerns, or they ask why you're asking, you can tell them you feel the project is taking a bit longer than it should and you wanted to get their thoughts on the matter. From there you can possibly also ask whether there is perhaps someone available to provide some "guidance" or "help".
Although it sounds like you're fairly close to finishing the project, so I'd be surprised if they're provide someone to help you (unless it's just a question here or there for which they don't require knowledge specific to the project, but it doesn't sound like you need that).
For what it's worth, "each fix reveals one new issue I hadn't thought of" sounds like software development in a nutshell. You might be worrying for no reason, but it's still a good idea to check in with your manager.
Also, have you heard of imposter syndrome? If your manager is giving you positive feedback, it's possible that the only issue is with your own mindset.
