Don't lose any sleep over this revelation. More than half of all people have a leg length discrepancy to some extent. But unless its a pronounced difference -- or you are currently experiencing hip or knee pain -- there's really no need to "fix" the condition.
In the majority of instances, a difference is attributable to spinal misalignment and muscular imbalances (rather than a true bone length discrepancy). If needed, a local chiropractor can quickly sort this out for you.
Lifts can be very useful. But automatically putting a lift in your shoe without a spinal examination won't necessarily correct the underlying reason for the "short leg", and could propagate new issues.