Hi phdapplicant. It's normal to have reservations about accepting the scholarship. You can always accept it now and turn it down later if you get one for another university. I don't think it's like signing a legal contract. Normally all the official sides of things will be worked out later (i.e. just before you start your PhD), so you probably have enough time to look for another scholarship at a more suitable university.
My experience of applying to do a PhD sounds like yours - I received a scholarship but the university wasn't as good as my previous one. I never bothered applying to other universities. In many ways I regret it now but was naive to the signficance of this at the time. To cut a long story short, the new university lacked many things I was used to and indeed required for my research (proper expert support, the right equipment etc), so I had to compromise all the time on my research.
My advice: think carefully where and who you are going to do your PhD with BEFORE you consider the money side of things. In one of the best departments in your subject, you are more likely to come across great opportunities during the PhD to put on your CV and help your future career.