If your teacher tells you that you can't enter the Standard class for Maths, not because your grades are lacking, but because the class is apparently "full," tell her you will sue the school and you have the right to do so because she is misguiding and misleading you as an educator.
Maths Studies is a joke of a class and that is universally attested. There are always those group of students who are either a) too lazy or b) genuinely horrid at Maths and cannot cope with it to save their skins. Maths Studies is designed for them. It is most definitely not designed for students who get As in their GCSEs, you could easily manage Maths SL.
In the US, if you have a Studies credit, they make you take loads of classes (in some Universities up to 3-4 semester's worth of Maths) to catch up. In the UK, while your SL subject choices don't make as much of a difference, it's safe to say that if your preferred University had to come down to a decision between picking you and picking another student with a similar prediction for the same course, but that other had Maths SL while you had Studies, rest assured, you will be rejected.
For certain courses in the UK, the SL or Studies class doesn't make any difference: these are generally the Arts courses. For Engineering, even Medicine, or anything Science-related really, SL Maths is expected at the very least, even at the lower-tier Universities. Even for some Social Studies courses, top Unis expect you to take SL Maths (or HL for Economics and Accounting and Finance). When I applied for Law, King's wanted me to get a 5 in SL Maths as part of my offer and Warwick wanted me to get a 4. Maths has nothing to do with Law, yet it was in the offer alongside an English requirement. I don't understand why, but it matters.
You tell your Coordinator that he/she is screwing with your future by putting you in Studies when you can clearly handle the workload in SL and denying you that opportunity due to "scheduling" issues simply displays his/her ineptitude as an administrator in meeting the academic needs of students, which is why you're paying the effing fees.
Honestly, putting a perfectly capable student in Studies because the class is full...the nerve of some people.
Stick with Business if you want to, but make sure you get out of Studies!
Chemistry HL is widely regarded as one of the most difficult IB subjects, right under Maths and Physics HL. It is really, really hard. There's nothing more to it, you have to work in that class and constantly keep up and the lab work is pretty intense, but you have to push through with it.
Having two HL Sciences is an uphill battle, but it isn't impossible. Thousands of students the world over take two HL Sciences along with Maths HL every year and many of them succeed and do exceedingly well in the diploma. Don't let the challenge deter you, relish it, because if you don't relish it, you will cry, a lot.
Honestly, if you're keeping B&M, bring it down to SL, that's the only advice I will give you on that front, the rest is up to you.
Arrowhead.