I emailed a professor asking him to be my master's supervisor. He replied saying he is willing to meet me and asked me to send him my transcript. I have sent it and he has not replied yet after a week (he replied to my initial email a day after). I don’t have great grades so does this mean that he's not interested anymore?
Any answer to this question would at best be a guess.
It doesn't necessarily mean that he's not interested in it anymore. Perhaps the professor is just busy. Maybe he read your email, thought he'd get back to it later and then forgot about it as more emails piled on top of it.
It's been a week since your last email. If I were you, I'd email him about this. That's the only way to know. Bite the bullet and send that e-mail now or a couple of days later asking if he is okay with your transcripts and if you could meet him as discussed. The worst that could happen is that he'll reject you. He won't be angered if you send him an email asking for clarification.
Academics tend to be busy people. The pathway from submission to publication of a journal paper, for example, can typically take 3-6 months. I recently chased for a status update for such a paper after waiting 12 weeks without word.
Given it's been only a week, perhaps wait another 2-3 weeks before approaching the professor again, and be sure to be polite.