Hi,
I just share my opinion with you based on my past experiences. Hopefully, it able to helps you to make the right decision.
1) Strong fundamental Mathematical and statistical knowledge is required if you wish to choose MSc Statistics. Not only multivariable calculus, but you also need to know some Linear Algebra, Multivariable Probability, and some Applied Statistics Methods, such as ANOVA, Regression, Time Series, Multivariate Analysis, etc. I think these methods are most likely will be covered in your Econometrics courses.
2) If you wish to take MSc Statistics, the statistics courses that are covered are not only in economics but also in wider fields. Unless if you are taking the MSc Statistics that is offered under the Faculty of Economics. In econometrics, the statistical methods that you learned might be more applied, but in Statistics, it might be more theoretical and you will be taught to solve the statistical problems in more mathematical ways. These all depend on the university's policies. Different universities might have different policies in offering the courses.
3) Are you going to choose your MSc Statistics in coursework mode or research mode? If coursework mode, try to make research, see what courses are offered for that MSc program. If you are able to discover the course description, it would be better so that you will know what topics are the course is going to covered.
4) If you have friends that studied in BSc Statistics or Mathematics, you may ask them what courses that they have studied in their program. You may also borrow their study notes and discover yourself or can seek help from them. It is better to make proper preparation before you enroll in the MSc. I have also done the same before I enrolled in my MSc Statistics and it helps me a lot.
I am just sharing based on my past experiences. You may get advice from your lecturers, seniors, or see whether there are other experiences people reply to this post so that you can refer to their advice as well.
Thank you.