I was born with fetal alcohol syndrome. Does this affect me mentally?

It Is Likely. The effects of fetal alcohol syndrome can vary in severity from one person to another, but FAS commonly causes a variety of problems related to learning difficulties along with other behavioral and emotional problems.
Yes. Usually there are developmental delays. This varies in each individual. Usually special ED classes are needed.
Yes. Fetal alcohol syndrome has been attributed to low birth weight, some dysmorphic features and even mental retardation. Depending on the severity of alcohol exposure, the severity of the presentation can be variable.
Maybe. There are 2 basic variables in biology: environment & genes (susceptibility). In your case, alcohol exposure was the environmental factor. Your susceptibility to its effects are not known. Therefore, there could be severe impairment to no discernible impairment in your case. The risk is high. That's why we caution against its use in pregnancy. But the two major variables remain in each case.