Hey hun ((Hugz))
First of all YAY CONGRATULATIONS!!

You ACED the interview and got the job!!
I have a feeling people who are kinda shy and reserved get to come across great at university settings...
Think about it, most professors (except for the ones with giant egos, and even those) and students may be rather reserved themselves, study-ish type etc.
If it's part-time admin work or such, they are looking for someone who will fit in nicely (and probably not some too loud obnoxious type) Shy people can be kind, caring, observant, and this makes for great customer service too!!
I think it's good to try and experience this job first, and then later decide whether you'd accept a longer position there... all sorts of factors can be important - how you get on with coworkers, how you actually like the job, are you a good fit with your interests and skills, how the pay is, what other options you can get...
Where I live library jobs are not so easy to come across, there's some certification and experience necessary, often, many people are after these jobs so they take on someone who was previously employed there via another program (or had student work/internship or such there) or people with connections. You can do some informal networking and find out what education/courses are needed for library work where you live...
Some people online (from US?) said for some positions MA might be needed? Check in the libraries where you might be interested to work, maybe offer to volunteer there, make friends with librarians...?
It sounds like you are quite young, you can try this job for a few months (or a few years) and you can have bright hair later on too... You can maybe accessorize in a 'cool artsy offbeat' way? (Or just live that lifestyle in your time off or in holidays?) You can transform 'normal hair' into more 'out there' with accessories or wash-out colors (check how long that stays in)
Also remember, most hair colors (except maybe henna) are somewhat toxic for the person and environment, and piercings can mess with your body-mind system too... What about 'fake' piercings, if you must? (clip on thingies)
Maybe research the colors and other options?
You could maybe even tell them (later - *when/if* they ask you to work there for longer!) that you might wanna try out some different positions (maybe they could even help with that, if they genuinely like you?) and that you had a great time there and loved working there and would be happy to work again, or introduce a new student into the work, depending on your schedule/timelines... or something like that?
(You could later even maybe do some part time work here, some part time work in a library... there are probably many options out there, not just 'either-or', also 'and' can maybe be possible...)
Take care hun & fingers crossed for ya!!

GO ROCK THIS PLACE!!
PS There are books and websites with info on how to do great customer service, do great at your job and improve communication skills etc so you can get into some research too

check what's in the libraries?