2nd year entry CS at St Andrews

I just received an offer from St Andrews for CS in 2026 with first year entry. I know now that I can't change to second year entry yet and have to request it when I arrive. What are my chances with this? Does anyone know what they base their decision on? I think St Andrews would be my first choice but I don't want to do a 4 year course since I've already taken a gap year, I was just told to apply for first year and then try and switch after I got a decision.