If you don't want to go to the other unis that you applied for then the decision is pretty much made for you, it's either ditch Sheffield and not go/reapply next year, or take a gamble on Sheffield.
Sheffield is not a bad city, it's fairly cheap to live, there's stuff to do, students seem to like it, but then it's not the most grippingly exciting city in the UK. But it's not one of those marmite places that some people love and others hate.
Travelling from London is not that bad, its a couple of hours, if you book early enough you might be able to get a cheaper train deal.
If you really don't want to go then just accept its a risk, there might be things that you find when you get to Sheffield that you don't like, that you would have realised had you gone up and visited, but they might be things you can live with anyway.