You have not moved the shape by the correct amount.
The line of symmetry is shown by the dashed line.
If you imagine that there is a mirror on the dashed line, the correct position of the reflected counters will be where they are in the mirror.
If a counter is 3 squares away from the mirror line then its reflection will also be 3 squares away from the mirror line. If you turn on the guides and click on the counters that are already placed you will see a guide showing how to work out where the reflection should go.