Many of us started out by taking jobs on units we didn't particularly want, and then made a change when the opportunity arose. There are many factors to consider in making the decision. It can be a good way to "get your foot in the door" at a hospital you really want to work at, but which might not have an opening right then in what you want; and some hospitals won't hire new graduates into some (or all) specialty areas, but want you to get some general (med/surg) nursing experience first; and it may seem more appealing than being unemployed while waiting for your "dream job" offer to materialize!
I can think right away of two experiences in my career -- when I was getting ready to graduate, I applied to the hospital that sponsored my diploma school. They offered me a job, as they routinely did to "their" graduates, and asked me what unit I'd like to work on (of the units where they had openings). I chose to take an open position on the urology floor on the shift I preferred, and thought everything was a done deal. During the time between when they offered me the job and when I actually graduated and became available to work, the nursing office called me in and explained, v. sheepishly, that they had received an application from a nurse who had a lot of experience in urology and wanted a urology job, and they wanted to offer her the job on the urology floor -- would I be willing to please take an opening on one of the other floors? I probably could have made a stink about it and refused to cooperate with them, but would that have really benefitted me in the long run? It didn't really make a lot of difference to me; I knew I wasn't going to specialize in urology for my career, and I was just looking for a job to get some experience and support myself while I looked for a job in psych. So I agreed, and took the orthopedics job that they wanted me to take.
Several years later, I applied to the VA hospital closest to my home. At that point, I was an experienced psych nurse; I indicated on my application that I was looking for a psych job, and I was interviewed by the psych supervisor. When the 'phone call came, the nursing office offered me a job on a general med/surg unit. I agonized over it for a few days before I decided it would be worth it to take the med/surg job to get away from my current work situation, and to get hired by the VA. It was only after I was hired and working on the med/surg unit that I found out that that particular VA (or maybe it was VA-wide policy at the time) only hired into the med/surg units and only "promoted" to the specialty areas from within -- if I had turned down that job and waited for them to offer me a psych job, it NEVER would have happened ... So, I worked med/surg for a few months, got some great experience and brushed up my skills, and, as soon as there was an opening in psych, I applied for it and got it (which had been the nursing administration's plan all along).
Only you can decide how "picky" and rigid you want to be, but remember that, as a new grad, you are competing with experienced RNs for the more desirable and specialty areas. If you decide you will only accept your dream job, it may be a long wait. There's nothing keeping you from continuing to look for a "better" job while you're working ...