This riff is a little trickier than it seems at first glance, (or listening). The key element(surprise, surprise:p) is rhythm. You must practice this keeping everything as tight as you possibly can and at this point, there are no drums to guide you. Practice it as slowly as you can and be sure to really emphasise the last 8th note at the end to really get that tightness.
Well done! As always, use the backing track when you feel that you are ready for the full tempo version. Post an mp3 or video of your performance in the forums, whether its the full piece or just part of it, so that everyone can check out your skills. Rock on!