How badly will a master's thesis plagiarism report affect my career?
Any answer will be opinion-based, so here is my opinion.
If you already got into a PhD program, just move on and focus on your current research. The odds are your upcoming contributions will be the key documents defining your career for the years to come. A master thesis, in my opinion, won't be really examined by anyone. Yes, sometimes you find a truly outstanding master thesis, but usually it is just a mildly original compilation made by a fledgling specialist, written with a sole purpose to prove that its author deserves a degree.
In your case the plagiarism you mentioned does not touch the core contribution. Too bad you copied some text verbatim without using quotation marks and endnotes. However, it doesn't invalidate your results, which are the main basis of your degree.
If you feel really scrupulous, I'd advise republishing the &quot;corrected&quot; version of the thesis -- at least, put it on arXiv. Probably, you have other flaws here and there, and if you believe your thesis is worthy, it might deserve a certain minor makeover. Just do it without much delay, and if someone ever questions your thesis, you'd be able to point out that there is a newer version long available, and there is little reason to peruse earlier texts.
A side note: your fault was overlooked both by your supervisor and the referees. It happens.