converting to an stl file changes model shapes

Hello I’m using creo 10.0 student version,( I’m new on the platform it’s been a week-since I started) the problem is while converting my .asm file to an .stl file my parts size change for example I have a semi circle in the model it is shown as a cone (I shared a pdf of the image) now what should I do. The image is from pre foam.(the model is for 3D printing)