The BSc is not a vocational degree (similar to the BA, BBiomed, and BEnv), so it's not geared to land you a job in a certain area of employment. The degree is designed to give you a set of generic skills that will benefit you in the workplace, including improved writing, listening, critical thinking and creative thinking skills, as well as discipline-specific knowledge that may prove useful for postgraduate studies. However, your degree is only a piece of paper and it's not going to get you any job without further effort.
Postgraduate studies are definitely your best option if you wish to work in a science-related field in the future. You mentioned lecturing as a possibility, but keep in mind that academia is an extremely brutal profession to break into, especially right now. Don't just assume that you're going to land a lecturing job automatically once you've completed your degree. I was considering going down the academia road with my BA and had full intentions of going on to study a PhD, but I decided against it once I discovered how piss-poor the job prospects are in academia and for post-doctoral students in Australia more generally.
If you don't mind the stigma that's attached to the teaching profession currently, then primary or secondary teaching could be an option for you as well. Again, that requires graduate work. I'm studying the MTeach right now and I'm loving it, though it's definitely not for everyone.
Also, just because you're studying a BSc doesn't mean that your employment prospects are limited to science-related areas. One of my friends landed a managerial position at a large company with his BSc, for example. The most important thing that you can do right now is to keep your options open and make connections through work experience, volunteering, etc. At the end of the day, those are the keys to gaining employment in any field.