Don't be disappointed! My first flush was similar to yours--took several bm's to get out about 45-50 small green stones.
The second flush got out about 200 lentil-size stones.
Last night did the third flush. Wow! Only one bm so far this morning but one stone was very large. I was so excited I forgot to count how many others were in the toilet.
Waiting for more now.
Just try again, they told me here that the flushes get better and they were right.