How to increase object detection in one class?

[seon-creator]

I'm doing instance segmentation for detecting some spots and counting them from skin images.
This case make automatically bounding box, so I can train this data to mmdetection.

I made one category named spot, and make other instances like this.

I'm using YOLOv3 model.
And then test the model to imgs.

I count the objects and find that this model limited to detecting 100 objects.
I want to increase more than 100 objects.
How to increate detect objects?

I tried change threshold but it is same result.