From what I have read on neck tension, and my own experimenting, they would be fine to shoot. Although the necks were undersized the bullet itself will re-expand the neck when seated, the brass can only maintain a certain amount of tension, not much more than .002-.003. Try this, run a case through the die with the too small expander and measure the neck, then seat a bullet and measure, then pull the bullet and measure. I think you will find that after the bullet is pulled, the neck did not "spring back" down to it's original size but will be where it should be from using a properly sized expander, only you used a bullet to expand the neck.
Or just measure one of your loaded round then pull the bullet and check, it'll most likely have the .002-.003 tension. If it all checks out, I wouldn't bother starting your loads over.