If you are pressing without heat, you need to put your flowers between two layers of paper towel (viva is good, as it has no pattern) and then put that into an old telephone book and then weight it down good. Give it several weeks.
On the other hand I use my microwave.
I take a old hard bound book, use the two layer of viva and put my paper/flower/paper into the pages of the book and then microwave at low power for 2-3 min. Then let it cool under weight. You may need to let it dry a little more, but not the two weeks, maybe over night or several days
Good Luck

I wonder if your flowers were damp; that's the only thing I know that would cause them to rot. Pick the blooms after 10 am or later so the sun has dried the dew. Don't give up-flower drying and pressing involves a lot of trial-and-error, but the results are worth it.

I'm sure you've solved your problems by now, but for more info that you might find helpful ask for the free downloads on pressing and making cards at my website www.sonshinecrafts.com

Here's how I press flowers successfully. I use an old phone book. Begin about 100 pages from the back. Fold down a bit at the corner. Continue coming forward and fold down a corner every 50 or 100 pages. The corner folds will help you locate your pressed material.

Now you are ready to gather flowers in the morning without any moisture from the dew.

Pansies wwork well. Any blossoms that are thin and flat. Pull the petals from flowers with thick centers such as daiseys or carnations. Leaves can be pressed, too.

At the back of your book, arrange a single layer of blossoms or petals. Carefull cover with the next section and hold firmly as you arrange the next layer of floral material. Continue. Then place a flat weight of 10# or more on the book. It takes at least 2 weeks, so wait to check.

Don't know what it is about the paper or ink in the phone book, but I have used my books repeatedly and have never had the paper wrinkle or the ink come off on the floral material.

Hope this works for you.