Given the fact that you are only familiar with the basics and think that you may struggle, perhaps you should consider taking Mandarin ab initio? Essentially, an ab initio course is a language acquisition course for students with no prior experience of the target language, or for students with very limited previous experience (the latter seemingly being the condition that applies to you). If you end up choosing to pursue Chinese, a good start would involve accessing the Notes & Resources section, precisely the following Chinese in Context resource:
ummmm yep, there were like not chinese in context notes here when i was doing hsc, so I decided to drop some here before deleting them.
Despite this being a resource that targets an HSC subject, the content itself may be useful in terms of supporting your IB journey.
Additionally, I suggest having a look at the Tutoring Classifieds forum, where you may find individuals that offer Chinese tutoring and resources that suit your needs, using the link below:
Looking for a tutor or offering tutoring services? Post a thread here!
Alternatively, should you choose to study another language subject that would suit your level of linguistic skills, you may wish to consider taking one of the subjects targeting easier European languages, such as Spanish, i.e. Spanish ab initio.
I hope this helps!