Hello Jason,
thank you for your help, but I think, that this is bigger issue, than it appears. My retailer changed this SE for a new one 2 days ago and the problem
with the gap is even wors on this piece. Moreover, the guy in the store has iPhone SE too and this problem is on his device too. So, 3 iPhones have 3 exact defects. This is not best result and best ad for Apple. I will change this piece asap and I hope, that I will get lucky. I am really fan of Apple products, but this is not quality, for which I pay. I am really, really frustrated. The only option for me is get my money back or get a new piece with 100% chance, that this defect will be on another piece....