You've already completed an interview full of technical questions, and they reached out to offer you the position - that alone says a lot about your ability to perform the job. That means you did better than all the other candidates, at least some of whom are probably "more experienced" than you. Clearly, the employer thinks you can handle it.
(I assume you were honest with the employer about your lack of previous experience during the interview.)
As a wise man once told me: 'When presented with a new opportunity that you don't know how to do, always say "yes." You can figure out how to do it later, the first step is getting in the door.'
The worst that could happen is you fail and get fired. If that happens, go back to applying for junior positions and explain to future employers that you thought you were ready, but you weren't. Recognizing your limits and learning to respect them is something employers will appreciate. Having the ambition to try when opportunity knocks is also something they'd probably appreciate. I don't think that trying and failing here will hurt your chances at another job, so don't worry about that.
TLDR; Do it. Nothing worth achieving was ever completely without risk.