Isn’t what you stated a “Theory”
Very informative.
Again educate yourself. The term theory in science does not mean what you think it does. Theories are not uncertain or conjecture. In fact a theory is pretty much the end goal of any science. If you develop a theory, you pretty much have achieved the pinnacle of your scientific discipline.
The term hypothesis better encompasses what most people think theory means. In actual fact a theory is a coherent explanatory framework encompassing multiple phenomena and backed by multiple lines of observational evidence. The Big Bang most certainly is a theory, but in this scientific sense.
Could it be wrong? Of course, but that is true of all scientific theories. If an observation is made (possibly by the James Webb telescope or by a future observation) that contradicts a prediction of the Big Bang theory then the theory will be modified or in an extreme case replaced by something else. That actually has already happened — the original BB theory did not include a period of exponential inflation and it had a singularity, a state with vanishing universal size and boundless energy. The inflationary period has been added to the model and the initial state is now a small, but finite universe with high, but finite energy, not a singularity. This has happened because we now have better observational data, such as a more refined measurement of the variations in the CMB for one example. This model is adjusted to be consistent with new data as it comes in. That is simply how science works.