almost everything about your post is wrong and i'm confused if you are asking this or telling others, if it is the later then you should first educate yourself before trying to tell others what bitcoin is and how it works!
Each Bitcoin is basically a computer file
No it is not a "computer file", you can call it a computer program although that is still a bad definition in my opinion.
bitcoin is a currency that using a peer to peer network and relies on cryptography to work.
which is stored in a 'digital wallet' app on a smartphone or computer.
"bitcoin" is not stored in your wallet. bitcoin is stored on the blockchain and if you run a full node you store the blockchain on your computer. your wallet only contains your keys.
People can send Bitcoins (or part of one) to your digital wallet, and you can send Bitcoins to other people.
correct but technically you send the coins to their address not to their wallet.
Every single transaction is recorded in a public list called the blockchain.
blockchain is not a "list" it is a "chain".
in a list item 1 and 2 have no association and list doesn't necessarily mean "order" so you can swap position of 1 and 2 without a problem.
in a chain however item 1 and 2 are linked and the order matters meaning you can't swap 1 with 2.
This makes it possible to trace the history of Bitcoins to stop people from spending coins they do not own, making copies or undo-ing transactions.
that is not the reason.
the way bitcoin prevents people from spending other people's coins is by cryptography that i mentioned above. it is called elliptic curve digital signatures which is required to spend from bitcoin addresses and only by having the private key you can spend those coins.
to prevent "undoing" transactions that are confirmed which is called double spending, we have Proof Of Work or PoW for short. again another form of cryptography that ensures the cost of replacing a block is too high and goes higher as more blocks are mined so that it becomes impossible to change the blockchain.