Mein's only previous experience of first-team rugby was off the bench against Hawick and Melrose in the RBS Premiership earlier this season, but last Thursday after training, head coach George Graham named his squad to play in the Pool Five encounter at Netherdale and selected him at number 10.
He said: "I have been in and around the fringes of the first team squad so far this season and it was good to get on against local rivals Hawick and Melrose. I expected to be on the bench again against Aberavon, so it was a bit of a shock when I was in the starting XV for Saturday night.
"Most of the time over the past season and a bit in senior rugby I have been playing centre, but it was good to have the experience of [Edinburgh Rugby's] Grayson Hart inside me at scrum-half and I think I played pretty well."
Having been educated at Gala Academy and played with the Gala Mini Maroons from a young age, Mein progressed through to Gala Red Triangle and Gala Wanderers and in season 2012/13 cut his teeth with the club's second XV. He added: "I have been playing rugby at Netherdale for as long as I can remember and was a ball boy back in the day, so to run out for the first team in such a big game really was a buzz. The crowd included my mum and dad and other family while my brother Kris was on the bench just to make it extra special."
Back-row Kris, 22, came on for the closing stages, meaning they were both on the pitch at the same time and made it a day to remember for the Meins.
Gala lost 31-17 and the young stand-off described it as "the most physical encounter I have ever been involved in."
He added: "The body was sore on Sunday and even on Monday when I headed back to work, but it is part of the sport and I want to be testing myself at as high a level as I can. I just hope I have done enough to keep myself in the squad for Sunday's visit to Leeds Carnegie."
Mein has earned honours for Scotland Under-17, was in the Scotland Under-18 extended squad and last week was called-up for the Scotland Under-20 training camp.
"I was brought in late on for the Under-20s camp for a training match and I hope by playing more and more in the first team I can push my way into the thoughts of the age-grade coaches.
"Certainly it is great to know that George Graham backed me enough to start me for Gala and I will just keep working hard."