A bit difficult to help without knowing where you are going wrong, but I will give you my tips of where most people go wrong.
You say you can't seem to line up the map and the ground, are you orientating the map so that your line on the map lines up with the fore/aft axis of the aircraft? If you are NOT doing this then try it, it should help a lot, but I will be surprised if you have not been taught to do this.
Don't OVER navigate, you should have some sort of system with a nav checkpoint every 6-10 mins, check you are where you should be at each of these, make any adjustments to heading/eta for next checkpoint, note when your next checkpoint is, then PUT THE MAP AWAY until about 2 mins before you reach the next checkpoint, then get the map and look what your next point is, then LOOK for that feature, this sounds obvious, but many people then keep looking at the map instead of the ground and miss the feature they are looking for because they have their head inside, having looked at the map you KNOW what you are looking for , having SEEN it, you can THEN, glance again at the map to confirm you have the correct feature, but you should not need to look at the map again until you are aproaching your next point.
Hope this helps. <img src="cool.gif" border="0">