Turn over the rug and lay it on the carpet.
How to get an area rug to lay flat on carpet.
Take a wet towel and moisten the areas where the carpet is curling.
Cut tape to fit each edge of the rug.
If the ends still curl up move to the next steps.
Apply the tape to the edges of rug.
Double sided tape could be used in place of the carpet tape.
Many times this will allow the rug to lay smooth for a while.
Then take an iron and set it to a medium heat.
Turn over the rug with the right side down.
This should flatten the areas out.
With the towel still covering the carpeted area hold down the iron and press.
The tape is double sided so after you have it positioned where you want you simply peel off the paper that is protecting the sticky side that will be against your carpet.
If your area rug is for a sitting area make sure the edges of the rug go under the sofa or chairs to help keep it from moving.
If possible help hold the area rug in place by setting heavy furniture on top of it.