Worth stressing that this is mostly a question about where and when, not about how adventurous somebody is. The people improvising successfully are usually travelling somewhere with slack in it.
What pushes you toward booking everything:
- High season anywhere popular
- Small places with few beds
- School holidays, festivals, public holidays: check the local calendar, not your own
- Anywhere with a single road in and one bus a day
- Travelling as a group, since two beds are much harder than one
- Anywhere you need an address for a visa or an entry form
What makes improvising easy:
- Shoulder or low season
- Cities
- Regions with a dense network of trains or buses
- Travelling alone
- Somewhere with a well-developed accommodation market
So the honest answer for your trip depends on facts you have and I do not. If it is somewhere busy in August, booking it all was correct and the flexibility was never really available. If it is a shoulder-season trip through mid-sized towns, you have bought certainty you did not need.
Either way it is not a mistake: a fully booked trip is a completely legitimate way to travel, and plenty of people prefer knowing. The thing to avoid is doing it by default and then feeling trapped, which is what your question is actually about.