First you need to map your 3 values 1-3 onto just two categories: positive and negative. For example, you might decide to call the 1's and 2's positive and the 3's negative. Or maybe you think of the 2's and 3's as positive and the 1's as negative.
After you have done that, you just need to count the numbers of the different combinations. For example, the number of cases where the real and predicted values are both positive is the number of true positives. The number of false positives is the number of cases where the prediction was positive but the real value was negative. And so on. You can use the crosstab function to get those counts, for example. Convert the counts to proportions of the total sample size if you want.
