I guess not
I guess not.and (I) don't think so.; I expect not.; I suppose not.; I suspect not.; I think not.
a vague statement of negation. (More polite or gentle than simply saying no. Frequently, in speech, suppose is reduced to 'spose, and expect and suspect are reduced to 'spect. The apostrophe is not always shown.) Bill: It's almost too late to go to the movie. Shall we try anyway? Mary: I guess not. Tom: Will it rain? Mary: I 'spect not.