Make sure you are completely flaccid, maybe even put some heat to it if it is really that small. Now from behind grab just below the glans and literally stretch it out as far as you can. Center yourself over a cushioned chair (don't use a wooden chair), keep it pulled while positioning between your ass cheeks. Now sit down gently. If you try moving your ass around after you first sit down you will probably have to start over. Once you sit you want your ass to stay put. If your pecker is under you, you are good to go. If your penis really is too small, then I guess your only option is to get it longer through basic stretching exercises.