there are many different weights of muslin- some are very thin- some are very heavy- and then there are the inbetween ones- it depends on what you are planning to use it for whether or not it is (substancial) enough-
if it is about the same weight as other cottons you have used in quilting projects it will probably be fine-
if it is a thin(loosely woven) mulsin sometimes washing/drying it in hot water will tighten up the weave some & make it better.
the greatest thing about muslin is it gets softer & softer with time- a great (basic) fabric. if it's not so thin as to see through it and you like it- it will be fine to use.