Why is most if the tub bare?

Half the tub is full of pins and the other half is essentially bare! Is it something I've done wrong? My other tub has lots and lots of pins all spread out throughout and I did them both the same way. Any ideas would be greatly appreciated

Half the tub is full of pins and the other half is essentially bare! Is it something I've done wrong? My other tub has lots and lots of pins all spread out throughout and I did them both the same way. Any ideas would be greatly appreciated