What Plagiarism level of master thesis is acceptable?
The turnitin tool is saying that it thinks 32% of the text of your thesis could have been taken from other sources.  

The software is a very blunt tool, and often has difficulty recognizing common turns of phrase and specialized terminology (e.g. I've seen "Without loss of generality we can assume that"  and "Traveling Salesman's Problem" flagged.)  It also doesn't recognize situations where there's a direct quote (properly delineated and cited) from another source.   

Thus it's necessary for a human to review the report generated by the software to see what's going on.  Without seeing that report, no one can give you an authoritative answer to your question.  However, in my experience, I've never seen a paper with this high a score that didn't have significant problems.  

To directly answer your question, no amount of plagiarism is acceptable in a master's thesis.