Close but not quite

I am a new user of the Aneros and am really starting to enjoy it. I purchased a Progasm, I know probably not the best starter model, and have used it a total of 4 times now. The first time I got nothing much. 2nd time a little bit of sensation. 3rd time I was really going and getting some great feelings but could not keep it. My 4th try was today and I was able to get oooohhh so close to what I assume is a minor orgasm (not a Super O) but could not get over the top. I was able to have the wave/feeling pass and then get it back and start to build but could not build it to a release. My session lasted about 1.5 hours today and I decided to stop. I am guessing this is common for new users but am curious if anyone has any suggestions. I have read most of the posts on here about relaxing and have tried it but when the sensation really starts to build I start to shake and really work the contractions pretty hard. For me, harder contractions really seem to produce and build the sensation better than the light movements that are described in some of the posts. Maybe my inability to push through is due to the harder contractions and trying to force it. Any advice would be appreciated.