One sample t-test, unsure of test value

I would like to use a one sample t-test where accuracy is 50-50..

The data is rated on a three point likert scale of 1-performed task incorrectly, 2 - performed task with minor mistakes, 3-performed task accurately

I have calculated the mean and standard deviation of my data and that is fine, I am just confused about what test value to use.. (newbie)

Do I use .5 as in 50% or do I use 1.5 as this is the center of the possible high score of 3 that can be achieved?