Other options to diluting:
1. Buy the one-litre pack.
2. Buy the ingredients to make D-72 (very similar to Dektol) from scratch, and then you can mix up precisely what you want and no more.
3. Mix a bull fatch and use it up. Print another shot too, or make contact sheets or other prints.
The stock solution will keep for a few months. You can mix up the 3.8-litre pack, and only use part of it. Dilute the portion you need to do your prints, and save the rest for another batch of developing in a week or two or ten.