Problem with sculpt tool

Hi, everyone,
I am making a couch from a tutorial, but i have problems using the sculpt tool. If i make a new plane it’s working fine, but if i try use it on my couch it does not. Here is the file (479 KB), if somebody help me i will be very happy. Thank you in advance.

Hi there. I checked your file and got some solution for ya, mate. In object mode with selected sofa press cntr+a and choose “Apply Scale” - this will fix the problem with nasty brush. Then go into edit mode, select all and press control+n to recalculate normals - ur brush will work as it should add and subtract accordingly and your trouble should be gone.

Oh, thank you so much. I forgot the scale. :(. Thank you, thank you, very much.