Wahlenbergia's are difficult to tell apart and the number of petals is not diagnostic. The size of petals relative to the size of the lobe (the bell bit where the petals fuse together) is, as is whether leaves are opposite at the base of the plant. One local Wahlenbergia is also yellow on the downward facing side of the petals. I can't be definitive but given that opposite leaves are present and the petals are double the size of the lobe this is most likely W. strict