Hi,
The tang is way too long. Two inches long from the barrel is plenty. It also looks better if it tapers a little. However, it looks like you are using a pretty skinny barrel, which may preclude tapering the tang . I draw the profile on a sheet of paper, making sure both sides are even, then I cut it out and glue it to the tang as a guide. If the tang design is not even it really shows on the gun. The drawing below shows a tapered tang
Here is one without the sighting groove. Although a hooked tang and breech, the proportions can easily be adapted to a plain tang.
dave