The problem is navigating
no, when I ask where is the problem, I want to know is the trouble keeping the heading? Reading the map? Recognizing villages? Timing? Like I said, navigation is a task that consists of many smaller tasks and you have to recognize at which tasks you fail at
Dublinpilot made a very good point about GPS and making mistakes by turning early/late. Keeping a record of your actual track will point out where exactly your problem lies. I had the exact same problem, I used a sportstracker app on my phone - not only it showed my route, it also recorded my ground speed which was handy assesing the effects of wind etc, I only needed one look at it and that fixed my problems for good