Msc Economics at Queen Mary

Not sure what you're taught during your undergrad advanced courses. Graduate level micro and macro are much more math-intensive than undergrad level courses. If you were taught topics like New Keynesian, Ramsey, choices under uncertainty etc. with uses of differential equations, probability theories etc., and find it quite manageable, you'll likely do pretty well in graduate Econ courses.
If your advanced modules weren't the real advanced ones, you could have a look at Romer's Advanced Macroeconomics, and Varian's Microeconomic Analysis and you'll know what you're up against.

Thanks, I have done New Keynesian and uncertainty with probability, but not using differential equations. So far my undergrad avergae is at 78%, so I believe I have adapted well to my course so far.
How is the job prospects of graduates from the Msc Economics course from QMUL? I'm planning on working as an economist in the private sector, such as jobs in Macroeconomic think tanks, competition law or economic research consultancy.

Tbh, I'm not from QMUL and couldn't say much about its placements. But it is definitely one of the most hardcore Econ MSc in UK (only behind Oxbridge, LSE, UCL, Warwick imo). It sounds like you're really into Econ research. Why not do a PhD? Msc is sufficient, but usually economist positions prefer PhDs.
But if you insist on working after the MSc, I think your priority is to ensure your research interest, and try to opt for related modules and maybe do a disso on the topic. From what I heard recently, there are more positions for health, energy, and environment economics than other fields, especially for Msc.