Son needs a second circumcision, is there any thing I should be worried about? Skin didn't get cut all the way off is circumsized but with extra skin.

See a peds urologist. Revision circumcisions are one of the most frequent operation performed by pediatric urologists. Too much skin is a frequent problem and can easily be correct with a simple outpatient procedure. Risks are involved are those associated with a general anesthesia and surgical risks (bleeding, infection - very very unlikely).
Seldom necessary. Always better to have a little extra, rather than have too much skin removed. Almost all "incomplete" circumcisions will look perfectly normal & well circumcised at puberty. Penile shaft skin is very loosely attached & gets pushed forward by pubic fat pad & is normal. Adesions may develop between previous inner prepucial skin & glans. They separate own their own with time. Only do if uneven.
Discuss with urology. Discuss operation with urologist so you will know possible side effects-complications of the circumcision.