If you use sectional track, you'll often find that it's difficult to make a perfect fit when your design becomes more complex.
Some manufacturers provide all sorts of filler track just for this purpose.
Sometimes you can make the track fit by using the play (wiggle room) in the track. While this can be considered cheating, sometimes you don't even notice that you're doing just that when laying real track.
In AnyRail, you can cheat a little bit as well.
In general, to close a small gap, you can often disconnect a stretch of track and rotate it one or two degrees to make your plan fit.