My "S" sounds a bit like "sh" or "sch" - I'm 21. Can I fix it?

My "S" has a slight "sch" sound. When I was younger it was a big, obvious thing - lots of other kids commented on it. ("See" sounded more like "schee"). Now, no one ever comments on it, but my parents tell me it's still there, but in a very small way. Is it too late to fix it? Should I go to a speech therapist or something?