Hi, thanks for your query.
You have not mentioned when exactly did the injury
there are two possibilities.
Rough top layer of the skin may be a part of the healing process where in fibrosis
and scar formation occurs.
Other possibility may be some part of glass may be stuck under the skin as you are thinking. In that case it has to be extracted out.
I don't suggest to do it yourself or someone's help as manipulating it might lead to infection.
You may contact a doctor who can examine and take it out under aseptic conditions.
Hope this helps.