In the Philippines, an academic thesis is named by the degree, such as bachelor/undergraduate thesis or masteral thesis. However, in Philippine English , the term doctorate is typically replaced with doctoral (as in the case of "doctoral dissertation"), though in official documentation the former is still used. The terms thesis and dissertation are commonly used interchangeably in everyday language yet it generally understood that a thesis refers to bachelor/undergraduate and master academic work while a dissertation is named for doctorate work.
Even if you used a quantitative research design, but failed to employ a probability sampling technique, there are still many perfectly justifiable reasons why you could have made such a choice. For example, it may have been impossible (or near on impossible) to get a list of the population you were studying (., a list of all the 20,000 students at the single university you were interested in). Since probability sampling is only possible when we have such a list, the lack of such a list or inability to attain such a list is a perfectly justifiable reason for not using a probability sampling technique; even if such a technique is the ideal.
It is likely, and advisable, that you will not wait until the end of your research before starting to write it up. You may be required to produce one or more chapters for assessment part way through your research. The process described above can be used for any individual chapter you are working on. It is important to be prepared to critique and revise your own work several times. Even the early chapters submitted for assessment, and passing that assessment, may need to be revised later on. This is not a failure, but a positive sign of increased experience and skill.