If your BTEC is the extended diploma then you may be able to get the foundation diploma worth 1.5 A levels, which you could use to get into a higher education course later on depending on your UCAS points. It is likely that you would have to get an extra A level or equivalent (possibly 2) if you decide to do this. With 2 foundation diplomas (if you did a year of another level 3 BTEC), you should be able to get into university depending on what you want to study and the entry requirements. Somewhere like the Open University has no entry requirements so you can still access higher education regardless, just that it's not the same experience and you would probably have to balance study with full-time work.
Obviously if you're looking to get an apprenticeship then most of this won't matter too much. It's just that with more level 3 qualifications you may be able to get a higher/degree apprenticeship instead of one at intermediate/advanced level.
As a previous poster said, speak to your school or college about it to check whether you would get anything from your course. Quite a lot of people leave after the first year for various reasons and they should understand that you're just considering your options and may not decide to leave.