Never done an IQ test - might be interesting, but it would have been more so to have one pre and post stroke.
if I take it and I score horribly low and think I’m dumb, will that have an affect on me?
Maybe, but for you at least, I don't think so. I know a lot of smart people, who are dumb at pretty much everything they try to do. I know some dummies who know how to use what they've got very well.
What is the behavior modification it projects into the future?
Exactly. It is all about behavior changes, not the score itself.