I'm not in a similar situation, but learned early in 1L I needed to work on interviewing. I've improved my results a lot, and the only thing that's changed is my interviewing skills. Here's my two cents:
There's only so many generic questions these screeners can ask and you should have all of them on lock by January. This will be the minimum interview expectation for everybody in your situation.
Get back on the horse and do more interview practice. Do it with many different people. I'm going to go against the grain and say 3 screeners with no CB should gently start concerning you, assuming these aren't super small satellite offices. If all of these were NY offices with large CB rates I'd be even more concerned. One silver lining of this weird OGI timeline is you have data NOW (3 dud screeners) that something isn't working BEFORE OGI even starts. Also, that something is apparently not your documents or grades. Do not shrug and give up improving two months before the OGI rat race even starts.
Use this as motivation to practice more. Record your answers to layup questions (why Law, tell me about yourself, anything on your resume, why should we hire you, or the "We like you to lead the conversation" interview style etc.), and the generic behavioral questions. Answer them all with a smile. I bet you'll be surprised after you watch your own answers, but it will help.
Prepare to be asked in a stressful way about your grades or if you're not on any journal. Own it. Don't ever EVER bring it up yourself. Hell people with good grades sometimes have to remind screeners (they see a lot of people in a day). In your case don't give them a reason to flip to the transcript. If they don't, BOOM you're at least median in their eyes. But, DO NOT deflect grades if you get asked about it. Say what you did, what you learned, and how you're applying that going forward, all with confidence. Hopefully your interviewer won't be that jerk, but if you knock a stressful grade/no-journal/no club or whatever question out of the park it will set you apart.
Some people have to work harder on interview practice, but at least you know this *now*.
Lastly, take any "you'll be fine" statements with a big fat grain of salt. This is a dramatically different hiring cycle and you might not be fine. So get motivated.
To end on a positive note, you may be surprised how far ahead you are in that you realize you need to work on this now. Some people realize this *during* OGI (seriously, it happens). Every year a good amount of LR/high grade people underperform, and every year a good amount of below median people overperform. You could be the latter.
You only need one offer. You're almost done. Don't give up.
If you're reading this as a 1L:
-Do interview prep. Don't throw away 1L SA opportunities by having the screener be your first practice. Also, at least the economy was still frothing during our 1L SA search so you should be extra motivated.
-Grades are important, but you'd be surprised how far a good interview can carry you once you're in the door, which you will see from some classmates (it happens every year).