Moneysaving Expert has comprehensive budgeting advice, so will help with a complete list of possible expenses so you can include those that apply to you, also with tips on how to reduce where possible.
https://www.moneysavingexpert.com/family/money-help/
But from your list, what I can see is that you rent is high compared with your income, so are you entitled to universal credit to help towards the cost? Also can you earn more or move somewhere cheaper (the latter being easier said than done, obviously).
I've also put some possible things to consider below:
Income : 3000
Outgoings
Rent :1650
Bills: 250 need to break this down, what does it cover. It would be water, council tax and gas/electricity as a minimum, so sadly I think it's probably more than this
Phones: 125 this can be reduced, go SIM only for about £7 a month max, buy second hand/cheaper Android phones and keep them about 3/4 years minimum
Entertainment
Amazon Inc kindle, prime, audible- 36
Netflix- 7
Aws/gcp- 20 Not sure what this last one is, but cut all these down so you're only paying for one or two streaming services at a time. Watch everything on one service, then move on
Transport
Bus fares - 200
Food
Approx 500 Might be able to shave a bit off this
Pocket money/ things for school
200 this is quite generous if just 'spending money' but probably a good amount to aim for if it includes things like school uniforms/shoes
That leaves - about 100?