2006 Impala gas issues

Suddenly i cannot seem to get my car totally full. User to be able to get gauge above full mark. Now won't even reach full mark. Also, out feels my mpg is quite of. Can anyone tell me what to check. I don't something about cars but i lost my husband last November and he was my know it all! Any help would be appreciated!

Could be a kinked or blocked tank vent tube, have that checked out.

Do you have any problems putting fuel into the tank? What I mean is, is it hard to add fuel to the tank?

If no, then you may just have a fuel gage/sender problem....