Congrats, it's a great start ! From my experience it's not so usual, unless you had work experience before (not internship).
In any cases, SBA is the natural progression after BA, and teams are usually excited to go throught since its their first promotion. In terms of expectations, its obviously higher but it general the transition is smooth. In particular, the followings are expected from SBA compared to a BA :
- More autonomy
- Higher analytics abilities : crunch, systematic cross check
- Higher exposition to client
- Opportunites of management : on some mission you may have to work with an intern to help you on your scope
Of course it's a challenge, but I would not worry too much, since you received this proposition it means that they evaluated your abilities. Furthermore, when joining the company the staffing is adapted to your learning curve.