You must be playing VERY softly, Ruth!
There are a couple of solutions.... On the left side of the G70, under the Master Volume knob is the Balance knob. Twist it towards 'Keyboard', and the ACC will drop down in volume (and you can bring up the Master Volume).
A more permanent solution, that you can save to a UPG is to change the piano Part's Key Touch (velocity sensitivity) to LOW (Menu>Split&Touch>KeyTouch) and save....
Hope this helps.
BTW, not to take ANYTHING away from this forum (I enjoy reading and posting here!), you will get answers faster and more authoritatively if you post your questions at the Danish G70 site (it's in English!);
http://www.selskabsmusikeren.dk/ One last thought.... be careful of making YOUR sound WAY louder than the accompaniment. There's always a tendency to want to hear ourselves loud and clear, but for it to be a well-mixed piece of music, you have to not swamp the backing. You can use the Recorder to do a quick reality check..... Record a short piece playing the piano and style, then listen carefully on playback. You'll usually find you are a bit louder than you thought you were!