Honestly, that's exactly how I felt when I was finishing my MS. I thought my work benefited no one, was pretty much already known, and was really low quality. I submitted it to my committee, and they gave me pointers on how to improve it, or at least qualify for why it wasn't perfect (remember that getting non-information from a study is still information. I studied samples from a lot of locations and most of them yielded nothing. It gave me no data to work with, but it was still valuable to the scientific community because the next person won't have to waste that time.)

I actually did an entire section of my thesis qualitatively when it should have been quantitative (I didn't really know what I was doing), so I prefaced it by saying something like, "This data is intended to be representative of a general survey of types of organic matter present and is not intended to give a quantitative representation of ratios of species." I knew I could have done better if I had been given the time, but that was the best I could do, and according to my thesis, the intention was a representative survey and not an in-depth statistical analysis.

NEVER FORGET THIS: You actually do know your research topic better than anyone else. Your work may not be perfect, but it is the best of humanity's knowledge in that topic and should be shared.

PS, if your advisor says you are ready to defend, you'll pass. Professors will not risk their reputations by letting their colleagues hear inferior work that they have advised their student to do. You just need to be prepared to defend by rehearsing your presentation and thinking of answers to questions your committee may have, and you will be fine.