There are two ways of viewing stereograms. The first one is to cross your eyes. I suppose that you use this way. In this way on the most of the stereograms the background is on the front. So if you want to see it correctly you should go deep in the picture with your eyes so that the focus to be behind the picture. You can try this first with your fingers. Put 2 fingers parallel and look something behind them. You will see that it is similar like crossing eyes. The more you practice the more you will be able to see them. I hope I helped.
its more natural to use the cross eyes approach. this is something your eyes are adapted for to focus on objects in the near field.
pointing the eyes the other way has no value in nature and is tricky. even knowing the intent, with cross eyes you can place your finger in the near field and move it until the image emerges in the background - the two parallel fingers trick for the other way is very difficult. it is counter to the nature of how eyes work.
i have seen this a lot. no photographic stereograms work this way that i have seen - presumably because pointing cameras the right way involves maths and tricks, but any seperated images can be used to cross eyes even if the cameras/images point the same way in 3d space, or even slightly apart... and as i say, cross eyes is natural and easy for everyone.