Hi Stefanie,
You could bring your hair length up a notch to have more density to the ends. It sounds as though you may need too if your ends are thinning. Be certain they are this way due to the layering and not splitting ends. If they are split, you must snip.
There are products that help with hard water, water with metallic properties, etc. I'm talking shampoos, etc. that would aid in ridding your strands of unwanted iron, sulfur, what have you, from your hair. Do you have a beauty supply store near you? Go in and ask for products for well water. (I am assuming that's what you have) The brands vary from area to area and right now, I am having a brain malfunction trying to remember one I have recommended. If it's not in front of me, I'm lost!
I would shampoo with this well water shampoo and experiment with curling your hair first. You may even want to rinse the shampoo out with bottled water. Gallons from the grocery store are fairly inexpensive for this step. Why wait and be down to crunch time one week before wedding. Leisurely get your hair in shape now.
Next, wrap damp, not wet, hair that has had some styling gel applied, with bendable rod rollers. Allow them to dry thoroughly. Finger comb and pull hair back with your preferred band. Next roll, and bunch curled ends to back of head and pin down only where necessary. May want a friend's help.
The applied curls will help give more fullness. If there still isn't enough density, purchase a hair rat.
Advice elsewhere in the forum
The above blog will help you understand that product and it's homemade replacement if you prefer that.
All in all, experiment whenever time allows for some curl. You may try a curling iron, yet I really think a good "set" is the way to go to enable your style to stay in longer. Try different types of curlers. Perhaps you have girlfriends who will lend you different types and help you with your experimenting? You will want a game plan to ease your mind come time for the wedding. And you will want to be sure it will stay in place throughout the ceremony and during all the dancing afterwards!