Hi, I had a similar situation in Tours, but was able to take a different tour. Here’s the details I wrote in my trip report. Check in with a Tourist Office. They had several options.
“ I had reserved a chateau tour with Acco-Dispo, but they needed more participants, so I switched to a tour with A La Francaise. For this tour, a couple from Ireland & I went to see the outstanding gardens at Villandry. Our guide walked us through the chateau to see the rooms and see the garden views. Afterwards, she provided a relaxing picnic on the grounds of Chateau L'Iselette. The first tour I had planned to take was going to be intense, covering four chateaus during an entire day. This half-day tour turned out to be the opposite - very relaxing, and I really enjoyed the chance to relax in the country setting and hear much more about living in France from our young guide. Villandry had been my top priority, and we had plenty of time there to enjoy the setting, arriving before it was crowded. (I had seen some of the other chateaus years ago.)”