Hi hun - funneling with a stitch is to be expected and completely 'normal' for us ladies with IC. The reason for stitching in the first place is because the cervix is liable to open around the 16-24wk mark. What the stitch does is to prevent it from opening any further, effectively keeping the cervix closed below the stitch, which is what counts.
I had funelling to the stitch from 25wks with the twins, and only had 2cms of cervix left, so yours is looking great. If your cervix had remained completely closed, then there would have been no need for a cerclage. I was funneled like this until I delivered at 38wks with 16Ibs of twin - the stitch did its job and prevented any further cervical opening.
Rarely some women dilate right through the stitch, but there would usually be accompanyng contractions and bleeding for this to happen. You have IC, preterm labour is a seperate thing and you would need to go into preterm labour to dilate right through the stitch.
Sometimes the funneling you describe can close again overnight, especially if your cervix is dynamic and prone to changing day by day. Hard as it is sweet, try not to stress - this is to be expected with IC xxx