That's (as I understand it) the way democracy works - vote for it and stick with it. Perhaps elections should be re-run if the party some people wanted doesn't get into power?
Democracy does not end with a vote. If that were the case, we would have an election, and the losers would go away, and not engage with the Government in parliament. As it is, we have a vote, but continue to debate. Without this, we would run the risk of taking a vote, and then even if it was a mistake, would have to go through with it. This is an irrational approach.
I should add that Sweden and Switzerland have both ignored referendums in the past, as they realised they were irrational ways to proceed. But they are still democratic nations.
We should have a vote on what type of Brexit deal on offer, and include abandoning it all together. The truth is that the 48% is now rather more than that, as there are people who regret voting leave. There are also people who don't like where Brexit is going (but still in favour in principle), who may decide they would rather stay than go for the type of Brexit on offer.
A no-deal situation is called a "cliff-edge" for a reason, so if it were just the deal or no deal, this is hardly a choice. We need a third way.
Another reason why we should include an "abandon Brexit" option in a vote is that it was a poorly thought out referendum, as there was no detail on what type of Brexit was on offer.
https://www.prospectmagazine.co.uk/...-swiss-the-brexit-referendum-wasnt-legitimate
All that said, I suspect we may just go through with it without a vote, find it sucks, and end up back in the EU in the long term (eg. 15 years), and we end up using Euros.