It might be that meditation for that long it simply not for you. There's no moral judgement or failure attached to it, some people's brains just aren't wired to be in that zone for so long. If you're really determined to meditate for longer, try guided meditations, or a yoga class that focuses on the mindful/meditative aspect of the practice. You could also try increasing the length of your sessions slowly, by just a couple of minutes at a time, so you might start with 5 minutes, then try 7 minutes a few days later, 10 minutes after that, and so on until you reach the length of time you'd like to be meditating for. Most importantly though, be realistic with yourself about what's achievable and sustainable. An hour of meditation that you hated and will never do again is much less effective than 10 minutes which you enjoyed and will do regularly.