Buying from goodwill?

my mom and i occationaly go every one to two months. I researched that the money goes to a good cause (people that have none). Usually we get many clothes for the great prices (non worn out clothes with brand names like jeans that usually cost $200 are just $2-$5 and stuff) and i never have to pay for my own clothes at good will (but at holister and aropostle i buy my cloths; i get an allowence) but some people who need clothes badly who cant afford much shop at good will...and sometimes i feel bad because they need it more than i do...;( i just went there and found a cute holister top...but some girl could have used that top..we also donate to good will. i just bought a shirt yesterday but i decided when i got home i dont like it so we will donate back to goodwill (my mom doesnt get mad at things like that..but an exspensive dress that cant be returnable...yea you dont buy that till u kno) but now i feel bad..is it bad to buy from good will when i dont need it?