Facebook SWE Internship first round interview

I'm wondering what is the criteria/meaning of the first-round phone interview for Facebook's SWE internship position? I just did the interview two days ago. I personally felt like a did an awful job - I completed the two problems but failed the follow-ups and the optimization the interviewer asked for. But now I also just received an invitation to do the final-round video interview. I'm just really wondering does this really give me a second chance? Or the first-round "weak-hire" (I guess) still make it unlikely for me to pass the hiring committee even with a second round interview? Thanks for answering the question! Hope you guys enjoy the rest of the day!