Hi Jane,
Yellowed leaves and centers in Rose Campion are usually signs of too much wet, yes; however, I have had plants recover from it. Much of that depends on how low the crown is in the soil though, so if it does seem too low you might scrape or pull away a bit of soil from as near the crown as you deem safe and on outward, gradually descending as you go, to form a cone-shaped depression around the rootball. This will allow spring rains to flow outward and away from the crown. Try not to loosen any soil around the plant, just scrape it back. Loose soil will just gather more water. If there's mulch around it, clear it away.
Good luck!
