Help! Step won't sit right on my carpet

[KimDW]

I have thick carpet upstairs and burber carpet downstairs. If I use my risers for my step the platform does not sit completly on there and it moves. So if I want to use my step I can't use the risers. Can anyone suggest something I can put under it to make it level and fit together? I've been folding up a dish towel in half and putting one under one side of the risers (on each end)and it makes it a little better but it still wobbles around. Any suggestions??
Thanks, Kimbra

 

[groundhog]

I use doormats (the ones with the commerical style carpet) tightly woven and no pile with a rubber backing.You can get one for 5-10 bucks