I am a UK student who visited Italy in July of this year. The validity of my visa was for one month, with multiple entries. The date of entry was 6/7/22 (Pisa) and the date of exit was 26/7/22 (Brussels), which was well within the dates of validity. Everything was done in haste, but it went fine and I got back to the UK seamlessly. Only recently did I see the duration of stay on my Visa sticker: 15 days!
This has made me very anxious, as I have made a terrible mistake. I need to know how to get past this. How serious is this problem? No one stopped me or asked me anything at Brussels Charleroi border control. If I plan to apply for a new Schengen visa, would I be rejected, fined, or banned? I hope not. Should I choose my destination carefully to avoid severe penalties? Would it help if I postponed all travel plans to Europe for a year? Any advice would help, thank you very much.
More details: I am Indian and a PhD student in the UK. I went to a conference in Italy and had flight tickets booked to and from Italy. I submitted them with my Visa application and mentioned a tentative plan to visit my friends and family in Paris (the reason for asking for multiple entries). The change in plans was because I ended up having to combine Italy and Paris together in the same trip as my PhD deadlines had changed, so there was only a single entry into the Schengen area, and I stayed in the Schengen area during the whole trip.
The validity of my visa was for one month
, OP stayed 21 days