Hey GB, haven't heard from you in a while.
It doesn't sound like you've done any harm. On your first refill, the thermostat was most likely closed so after it opened, the amount in the resevoir went down. Your second refill should have taken care of it. If it continues to go down, then you might have another problem.
Check your calendar and see if you and the hubby can make the Rocket Launch down in Maggie Valley the last weekend of Sept. Not too far for ya'll.