Then do your venting here and not to classmates. People who always insist they failed, only to do just fine, are incredibly annoying. It seems like every class has at least one.
Apart from that-you may need to work on this tendency to "catastrophize." Real world nursing is hard; always going to the dark side ("I'm a failure! I might as well quit!") is really unhealthy and can lead to a miserable existence and inability to find any fulfillment professionally, no matter what career you choose. In nursing, there is almost always room for improvement. You WILL make mistakes. You will need the resiliency to bounce back from these setbacks and not exaggerate their importance in the moment.