[UofA] The International Tuition Scholarship I got is smaller than the website says I should've got

The operative word here is eligible. Just because you were eligible for a $18k scholarship, it does not mean that you will get one because it is not a guaranteed scholarship based on if you have A your will get B.

The bigger issue is that you do not know where you stand in comparison to the rest of the pool. Remember there are a limited number of scholarships and as far as SAT scores are concerned, you were at the bottom of your band. Each school will do their own conversion of your grades.