Yeah it's totally normal, but once you get it, you'll be happy with it. Our brains have a way of adjusting us to be happy about circumstances we are in that are beyond our control, so unless it's a complete travesty (which shouldn't happen as long as you've researched your artist), you'll love it.
I would suggest deciding on a design and then hanging it up somewhere that you'll see it every day. After a few months (yeah I know you said weeks but just wait a few months to be safe... enjoy the anticipation), you'll have no doubt whether you want it or not.
Yes I was so scared/nervous when I went in to get my first tattoo in June I had turned 18 in March, but now I have the beginning of my chest piece. If you have a high pain tolerance you'll be fine. Also bring a pillow depending on where you are getting the tattoo Im have it done on my chest and will have to be in weird positions and it's really large only 8 hours in and the line art and and tiny bit of shading is done. Also drink lots of water and stay calm the more you move the worse it will be also you may not get a quality peice of work if you move due to moving it can cause jagged lines since the artist needs a steady hand. Also when getting a tattoo make sure you will want this for the rest of your life, think of jobs, family, and other factors when choosing something that will stay on your body forever unless you get laser surgery. Talk to your tattoo artist about the best placement of the piece and the pain that may be associated with the work in that area. I hope this helped.
yes if you have never been under the needle it can be something that can make you second guess your notion of getting one. it took some time for me to go from the thinking about it stage to the oh why the hell not stage lol lol. but once I set down in the chair the artist was awesome at talking to me and keeping my mind occupied , and that did help me through the whole process. I actually got two done in the one sitting.