You will get lots of different answers I am sure, but yes, there are loads of us who spend our whole lives in debt, even if only because of the mortgage, and the after effects of rash spending in years gone by. I must admit that in my younger years, I would shop to make myself feel better - but it isn't the answer, things don't fill gaps.
Can't you take the stuff back, if you still have the labels in it? Being boringly sensible, the £300 would be better spent towards paying off your overdraft or your student loan, at least to make an effort. If you have bought these clothes on an overdraft that you have, in effect, borrowed the money to have them - while you are getting a good deal off your mum and dad. I bet they could have paid off some of their own bills with that £300 - put yourself in their shoes and see how they would have felt with you bring home those clothes, while in the same breath saying that you can't afford to pay a proper rent for your bed and board. I wouldn't be very happy about your priorities.
If you get into a good habit before you take on your own place and other responsibilities later in life, it will stand you in good stead - I wish I had.