I have to put my hand up as someone who has flown a time or a distance instead of a heading.....on more than one occasion. Luckily I didn't infringe, and I quickly noticed the error, but it's a very easy thing to do.
I created my own VFR plog in Excel, and designed it in such a way that my headings and timings were highlighted, and this solved the problem. With the plogs I'd being using from my school, the mistake was too easy to make.
Making landmarks fit where you think you are, rather than recognising that they are wrong, is also something that is very easy to do.
I also agree with IO....a 72nm leg seems very long for DR.
I really think more emphasis should be placed on radio navigation when training. Not necessarily for navigation itself (no VOR-VOR type stuff), but used to confirm that you are where you think you are, at each of your waypoints.
dp