How to get to pace in your first research project?

You started only two weeks ago. Relax. The others with whom you interact have played a role in this group for a much longer time. Nobody expects you to immediately replicate their experience.

You tell us how you asked a PhD student for help, and this student was very willing to help you. In fact, they helped you rightaway, and it led to the desired result. This is how a group is supposed to interact, so that is a nice thing. You then do not manage to replicate their solution independently. But you are a Bachelor student and they are a PhD. Don't worry! Ask the same person for help again! Tell them: "Many thanks for your help last time; it was incredibly inspiring. I tried to learn from it by replicating your steps, but I get stuck in place X or Y. Could you perhaps show me how it works?" This implies that you want to learn (by far the most important attribute of a Bachelor or even Master student in a research group), and that you understand parts of the solution the PhD student provided for you but not necessarily all of it. Again, this is an ideal way to fortify collaborations within the group: you show that the help was appreciated, didn't go unnoticed, and that you want to put in the effort to truly understand the solution.

Everybody in your group is there to learn. This holds for the Bachelor students, the Master students, and the PhD students. Do not expect yourself, as a Bachelor student, to instantly be on the PhD student level. Instead, show that you really want to become a part of the group, and that you really want to learn. Your instincts seem to be right to succeed in academia, but you should reframe them: not instantly understanding everything is not a problem, but a desire to learn is an enormous asset. Productivity is less important than a drive to improve yourself.

I think the key words are in the first paragraph: "I'm doing my bachelor's thesis". The two Master's students and the PhD student have been in the business longer than you, so of course they are going to outperform you. It's no different from how you are going to outperform first-year undergraduates. The way forward is to keep at it, and you should get better naturally.

It's usually OK to go into the lab on weekends (it's possible you'll need approval however), but if you're putting in that many hours you might burn out. Bear in mind that it's one thing to be in the lab, another to actually be productive. Further, if you're alone in the lab, you won't have anyone to ask for help if you need it.