[Bob Bengal]

Welcome to the forum. Yes it is a bit height issue. Easy mistake to make, for the same joint you have to get it right twice. I think everyone has to practice to get started with dovetails. Use a lot of scrap or cheap wood, it's worth it.

Posting a photo of it would be good, helps people commenting.

 

[Bob Bengal]

I may have been too quick in my answer last night.

Most often with finished through DTs the end grain of one board is flush with the face of the other board. That is determined by bit height, can be tricky to get perfect, it is common to make the end grain a little long, proud, then after the joint is glued trim the ends flush with a plane etc.

But maybe you meant the pins aren't wide enough for the gap between the tails? That would be a jig/template adjustment. Some photos would be great.