Hi Tom, I hate to say it but Walther's decals never were the best around. They use/used a low grade decal paper and the carrier coating on it was very thick. Perhaps if you let it sit overnight it might staighten up. It will looked wrinkled for the longest time until completly dry.
Strange as it may seem though Walthers Solvaset is in my opinion the best setting solution there is.
I don't know what your experience level is with decaling but when you apply a setting solution to a decal it turns the carrier film (which is actually a lacqure coating) into a semi liquid so the decal will snuggle down over details such as rivets and etc.
Here's a few tips:
1. Position the decal using water and a brush. Then blot up all of the excess water with the edge of a tissue...yes toilet paper works great
2. Do not attempt to brush the solvaset on.... I use a glass applicator from an old iodine bottle...ask the druggist for one.
3. Be sure that your car is laying on a flat surface and apply the solution around the edge of the decal first so that it will flow under the decal.
4. Very gently apply some more solution to the decal's surface without disturbing it and blot up any excess solution with the edge of a tissue but be very careful not to disturb the decal.
5. You will notice that the decal starts to wrinkle and deform. DO NOT try to remove these wrinkles...they will go away as the solution dries.
6. Just walk away from it until it is totally dry. This may take anywhere from and hour to all night depending on the quality of the decal.
7. When the decal is dry but shows a whiteish fog on it repeat steps 3 - 6 again. If the decal has bubbles in it gently prick them with a needle and then go with steps 3 -6 again.
8. When the decal has adhered correctly it will appear shiney and is ready to be overcoated with a spray flat finish.
Bear in mind that decaling is a "learned art" and it takes some practice. Once you get the process down you cant tell the lettering from painted on. Also remember that decals do not adhere well at all to a flat or semi flat finish. If you have painted the piece with that apply a semi gloss spray over it and allow it to dry thourghly before decaling. The gloss will dissappear with the final flat finish to seal the decals.