This is totally fine. If you really feel bad, you could explain to them you'd love to have them but your budget only allows inviting a small number of people.
Many people also have a brunch the day after the wedding. Maybe you could invite a handful of people who couldn't make it to the wedding and do a casual brunch or small get together?
I've tried so many times to read this and can never get past the first couple chapters. Just doesn't keep my attention.