Not even in nesting yet and feeling overwhelmed

I’m still in training for a work from home customer service representative insurance job. Last week they had us do calls for a couple hours to get us prepared before we go into nesting. It was so overwhelming that as soon as one call ended another person was already on the line. I’m overwhelmed because I didn’t realize that I was getting into a call center job. I was expecting just an insurance job. But now I’m getting scared. I don’t think I have what it takes to be on the phones nonstop for 8 hours a day. Call avoidance is a big deal and we have to answer these calls. I’m just so overwhelmed. There’s not even a minute in between calls. Any advice would be appreciated. How do I prepare myself for this?