very bad idea to come here on a tourist visa to get a job. difficult to transfer a tourist visa to a work visa - authorities dislike this a lot!

you are better to leave qatar and apply whilst out of country so things are 'above board'

ALso, final note, I am very surprised that you got a job offer, they do not normally hire expat grads with no experience (which I assume applies to you) because they have a lot of their own graduates who have the same education and experience as you and they will always be given preference.