For August/Early September, sounds like you're doing fine. (Do you have any clue how long your days will be on the tour? Or, are you just going to explore and go with the flow?) If you have a route and definite places you are going to stay, so known distances each day, and if there are some long days, you might try some longer rides of comparable length and terrain, on the weekend.
I'd recommend not trying to keep to a rigid schedule. If it is beyond your capability, the whole tour can become a bad experience. Our best adventures have been when we had plenty of time and no place we HAD to be on any given night.
Training is good, though, and we aim to get a lot of miles in our legs before a tour, but there was one year that it was so rainy, here in Juneau Alaska, that we were both rather out of shape at the start of the tour (in British Columbia). We planned some fairly short first days with the intent of riding ourselves into shape. It should have worked, but bad info from the Canadian tourism folks left us facing a 75 mile day on day two (twice as long as the info we had said it would be). And, no options for stopping along the way, it turned out (well, there were some campgrounds down dirt roads some unknown distance off the highway). We got into the second night town/campground pretty tired, but not shattered. The next day, we woke up feeling OK.
I would suggest that you ride your bike for the fun of it. Throw in some longer rides, if you can. Then, start the tour with shorter days to see what you can deal with riding a loaded bike on the actual trip.
We are aiming for a month in southern France in September. My wife had been riding 15-25 miles every chance she gets. I have more day time available and have been riding hard and easy from 15-75 miles, usually in the 30-40 mile range. I like riding my bike and being fit. I don't view bike riding as training for anything, just a joy. On our tour, I envision days ranging from 40 km to 75 km loaded. But, we're riding through the Pyrenees, so the climbs will necessitate less mileage. Weather, how we feel, some place interesting to spend some time at, may mean some days less that 40 km. It's possible we'll want to push 100 km for a day or so (not in the mountains). We'll see.