Don't worry about wasting resources. As you've discovered from the excellent advice above, if you don't use up the concentrate, it will go bad, so please go ahead and use it in whatever way produces the best print. That's what matters most.
As you gain more experience you will be able to tell when your print developer starts to go off, and when it does you will discard what's left and mix fresh. Before you ask, there has been numerous discussions here on the forum, regarding dividing the powder components into smaller batches and mixing half of it, or less, at a time. The consensus seems to be that if you have to do it, try it, but if you expect 100% consistency from developer batch to developer batch, it's probably not advisable.
Good luck, and have lots of fun printing!