When you say that you've "already done IT BTEC L3", was that a BTEC Level 3 National Extended Certificate in IT? Or was it something else?
You say you "want to take L3 course one year". As both the Diploma and the Extended Diploma are designed to be studied over two years, they'd be tough to complete it in one year. The Diploma contains fewer units than the Extended Diploma, so that might be a better choice.
Between the "IT BTEC L3" you already have (which I assume is an BTEC Level 3 National Extended Certificate) and an BTEC Level 3 National Diploma in Business, you'd have the equivalent of three A levels - which should give you a good shot at a university place.
Do you have any idea what you might like to study at university, or at which university you might like to study it? These are important questions, as not all universities / courses are equally welcoming of BTECs - so it's best to know sooner rather than later if there's going to be a potential issue.