A bit of comfort:

1 degree equals one mile at 60 nautical miles. This means if you are even as much as 10 degrees off of your planned course, and you go 60nm, you are 10nm off course. Are you able to see a checkpoint 10nm away? If you're high enough, absolutely.

Odds are you will only be about 5 degrees off of your planned course, so of your checkpoints are 20 miles apart, odds are you are only going to be a few miles off at most. Even if you missed 2 checkpoints, by the time you go 60nm on only ded reckoning, you're only 5 miles off. A few miles is nothing in an airplane. Again, though, altitude is your friend here.

Trust your headings, the winds will be close enough to the forecast to keep you in the ballpark. Every time I or a student felt like we were lost on VFR cross countries, the truth turned out to be that we were exactly where we thought we should be, we were just having trouble matching what was on the sectional to what we saw out the window.

Another common error: using airports as checkpoints. They all look the same, and are some of the hardest things to find if you don't know exactly where to look. Use geographic features, lakes, mountains, rivers, oceans, etc. if at all possible. If you have no geographic features, roads, cities, towns, etc. are my next favorite. Farmland can be a featureless desert, so more ded reckoning is required there, and usually you have to use the small towns, as otherwise all you have are square fields as far as the eye can see. Roads are a big help, here, too.

Good luck, and have fun!