Congratulations on your offer! Having studied HR myself, this major does not emphasise financial or mathematical aspects, meaning that the knowledge that you gained from HSC Mathematics Standard 2 is sufficient. While I did not study Marketing, I believe that the same also applies to this major, which makes sense since MQ states that, for both HR and Marketing, HSC Mathematics Standard 2 is considered assumed knowledge.
With that being said, it is still a good idea to try and improve your mathematical ability, as the level that is consistent with the assumed knowledge for the other Bachelor of Commerce majors is likely to be needed for a number of the units from the Core Zone, including:
- ACCG1000 - Accounting for Decision Making
- ACST1001 - Finance Fundamentals
- ECON1020 - Economics and Business Strategy
- STAT1250 - Business Statistics and Insights
In such cases, bridging courses are recommended. However, given your circumstances, it seems that your only option would be to work on improving your mathematical ability on your own, assuming that you do not wish to take a mathematics or quantitative methods elective unit (unless you have not considered this option, in which case you probably should). Studying on your own is not impossible, and has been done by numerous students. As long as you are committed and maximise your resources and use thereof (an example of which is BoS, where you can post any relevant questions that you may have), you should be able to improve to the level needed.
I hope this helps!