I am a UK resident holder valid until 2021 and invited by a family in Schengen and was given a Multi Entry visa from January 19, 2019 Valid until April 14, 2019 for duration of 30 days. NOw I entered Schengen January 19 and I changed my ticket back to UK February 18 which is 31 days if you count from January 19. I only realised just today that it is 31 days. I could not get an early flight now sinceI am booked/planned for February 18 and few hours left and cant get a flight early now

Thank you very much.
MJ