@skk - even I struggled with the buffer overflow material of OSCP and wasted most of my lab time.
I finally managed to figure it out when I tested it in my own lab and got a shell on the victim machine. Hence my suggestion, move on with the rest of the course and do not waste your lab time on buffer overflow exploitation. Once your lab time is up, you can focus on testing it locally.
CISM, CEH, CISA, ISO 27001 LA