there, alextro gave you a solution. When you're checking for collision it uses these poligons (polygon from your character vs polygon of your object of collision) to check if they have touched. if you use the one from upper picture, you can see it's polygon is not really as character is. so best to do to avoid simple mistakes is to use bounding box as shown on picture 2. later you can change that for better approximation around your char, but you have to do then pixel perfect collisions and more.
best you can do to try for now - use bounding box both on your player, and your object of collision - yes they both need to have good collision polygons for it to work nicely.