Major-General George B. McClellan to Edwin M. Stanton, June 27, 1862 – 8 p.m. (“Attacked by greatly superior numbers in all directions on this side; we still hold our own, though a very heavy fire is still kept up on the left bank of Chickahominy.”)
https://civilwarnotebook.blogspot.com/2014/04/major-general-george-b-mcclellan-to_6648.html
McClellan had a way of overestimating enemy strength.