Trafford, a former City academy player, returned to the club last summer from Burnley expecting to eventually replace senior No1 Ederson.
However, when the Brazilian left, City signed Gigio Donnarumma from PSG as their new No1.
"It has obviously been very up and down throughout the season because I haven't played too much and obviously I had a decision to make in the summer," Trafford told BBC Sport.
"Everyone always thinks when you make decisions (for) the best possible outcome and obviously it hasn't been the best possible outcome, but I have just tried to either improve every day and just try and stay positive, try and stay happy.
"Because throughout the year it has been such a big learning experience so the main thing I didn't want is for it to impact your general happiness and your general feeling. I have had to learn a lot throughout the year and I have just tried to work as hard as I can and try and improve and win the day."