These are my CX at 4 weeks. My wife hates that I call them "cankles" (look at the legs in the last pic- looks like CHF edema) or "toads" or "Chets" (after Wyatt's older brother in Weird Science when Kelly LeBrock turns him into a festering lump). She calls them BB's for Baby Broilers or "meat...
Every WL I owned have been slim bodied birds, lean and nearly breastless. I won't even cull them for people food when they "age out"; I run them through the plucker, do a rough gut (leaving the lungs and kidneys in) and quarter them for raw food for the doggos.
All my leghorns at this point...
If it is a CX, she'll take forever to begin to lay and the eggs aren't as big as you'd suppose. They are also not great layers- the one of mine that missed processing day and matured to the point of laying gave about three eggs a week. When I did end up processing her, she was massive. Her...
CX are usually fed meat bird starter and, later, meat bird feed with a higher protein percentage than chick starter/all flock feed only because they're supposed to be bulking up for an early date with the processing table. If you're not intent on processing it at 6-8 weeks and maybe put it off...
These are CX chicks purchased 7 days ago, probably two days old when I got them. They're unmistakable as CXs with their round butts, heavy bodies, chunky thighs and thick legs. It'd help if you had a pic of your chick standing on its own but I don't think you have CXs.