Colloquially, you are correct. However, in the scientific context that is not what a theory is. When talking about a scientific theory, the word "theory" does not insinuate any particular degree of uncertainty. Rather, a scientific theory is a group of propositions used to explain facts observed in nature. Whether or not it is accurate is ascertained by putting the theory to the test.
For instance, the big bang theory is not some gratuitous guess. It is the best model we have to explain the origin and subsequent evolution of our universe. It makes predictions, which can be tested. The overwhelming consensus from experts in the field is that the big bang theory has withstood the tests.

Here are some other examples of theories: the theory of gravity, the theory of evolution, atomic theory, the germ theory of disease, and the theory of limits. Would you relegate these to somewhere between guess and fact? I hope not, as the theory of gravity (probably the most uncertain of the theories presented above) explains the fact of gravity, the theory of evolution explains the fact of evolution, the atomic theory explains many properties of matter, the germ theory of disease is vital in medicine, and the theory of limits is the basis of calculus.

I think if one is intellectually honest, one has to admit to the possibility of mistakes. That said, the fact that our theories make predictions which match reality to a frightening degree implies that there is at least some level of truth to them. Would you agree with this?