But that doesn't mean that you shouldn't be allowed to fit in if you wish.
Fitting in means that the group is welcoming, that you are able to talk to people, share what you are doing and how you feel; it works both ways.
Fitting in is NOT being a clone.
Children who wear purple pyjamas to school and handmade shoes and who don't have a TV and spend all their spare time in the woods and take home-woven lentils for lunch can "fit in".
Children who have chain store uniform, brand name trainers, a Smiggle bag, a Jojo bow, and who watch all the same TV shows as the other children, can still not fit in.
And schools can be very cliquey or not. They can accept the child who's lived all over the world and never been to school, or reject the child they've been to nursery with who has the wrong brand of cheese on their sandwiches.
And really, if you felt so upset about having a different bag and shoes then either
a) they were specified on the school uniform list but your parents chose to ignore them (which is an entirely different issue) or
b) every SINGLE other child in the school went to exactly the same shop and bought exactly the same style in some hideous borg mentality (thankfully I doubt that's true - for a start, styles go out of stock and don't fit some children) or
c) you weren't the only child who had different accessories, but bullies decided to bully you and that was the thing they decided to use. If you had the same accessories they'd have decided your name began with the wrong letter. That's an issue for school to sort out and would not have changed had you had the clone bag and shoes. (This was what happened to me. Bullies decided to bully me, what I did was irrelevant, and school was completely ineffectual. I suspect this is what happened to you as usually that is the case with bullying that isn't intervened with). Or
d) actually you weren't the only child who had different accessories and that wasn't why you were bullied - but it bothered you more than it bothered the other children who had different accessories. So that's an issue with your confidence, and something for school/parents to pick up on, not an issue with the bag/shoes. If you had had the same bag/shoes, you would have started to fret over something else - did you have the same for tea at home as all the other children? Did you go to bed at the same time? Did you watch the same TV shows? In what other way could you be exactly the same but weren't, that would mean you didn't "fit in"?