Operababe - please do not worry too much. I speak from experience here as the mother of a 2 year old who has been in a nursery 8-6 five days a week since she was 6 months old. At the very same nursery there are quite a number of children who also do the same hours for 4 or 5 days a week - some of which I know quite wekk and in fact have also got to know their parents quite well too. All the children appear to be very level headed, sociable, confident yet sensitive to others needs.
It's easy for any of us to make generalisations here about what may or not be right for each others children, but for me, the key thing is knowing what you think your child will be comfortable with and knowing what you will be comfortable with..and then just forget what anyone else thinks as all of us can only really speak from the position of our own experiences (good or bad) and we do not know you, your child or the place you have chosen for day care. Ultimately, you are like me, you have to work for financial reasons, have family miles away and therefore have limited options available too you....and here starts the guilt trip!!
Now from my own personal experience, if you find a nursery that you are happy with, then I do not believe it will make your child more introvert - quite the opposite in fact. I also do not believe they will over stimulate your child - most nurseries have wind down time at the end of the day. I also think that in some cases a nanny or childminder might suit the siutation better, however unless a childminder only takes one child, they cannot offer one-to-one care either..and for me, I felt uncomfortable that there was a single person looking after my dd without any other oversight...but that was my choice.
All types of childcare has pros and cons....and no-one else can make the choice of what to do other than you. Let's face it, it's going to be hard to leave your dd irrespective of who is looking after her as she has been your world for the last 6 months....so please don;t make it harder on yourself....and please don;t worry about nursery. Many other parents have to do this too....