The UK polling booths closed at 2200 UK clock time so if you did not vote by then I am afraid you've missed the opportunity to influence the result.
The next big test for the coalition government will be the general election next year. It is quite possible that people will adopt different voting patterns then. The EU election will be seen by many as a chance to protest.
I have a sneaking suspicion that UKIP will achieve less success than some have predicted. I personally hope the Green Party has a good show and wins a few more EU seats.