I think we have really, really lost perspective in the UK of the level of expectations. An 'Instagram luxury lifestyle' isn't normal life for almost anyone and I don't think it was in the past either.
I presume the OP has a roof above their head (mortgage to eventually own, or rent), able to cover daily expenses, and her pension contribution has already been deducted before receiving her net salary.
What's the 300 pounds actually for, other than savings just in case? It's a luxury for the vast majority of people of the world, and even many people in the UK, to be able to save several thousand pounds a year.
300 pounds a month is half of many people's salary even in developed countries like Portugal, Italy etc.
It's good to have a rainy day fund, I have one, and I'd encourage most people to have one if they can afford it, but this asset accummulation, the expectations to have a large + nice house, a good car, annual luxury holidays etc... That puts you in the global 10%.
It's great that people with average jobs have 100K+ in savings, a house AND a pension in middle age, but on a global scale this is being comfortable.
For the majority of the world's population this isn't normal, 300 quid is a lot of money for them, and I'm pleased that it's possible to have comfort and security by working a normal job in this country. Count your blessings.