Don't sweat it. I find those Google interviews to be very discouraging and I felt dumb after not doing great on one when I was in school. Looking back, the whole interview was a mess. I got the call from the engineer 45 minutes late, I couldn't access the Google Doc because he was trying to send it to my university email address, and the coding portion started off with him writing "!(x & (x - 1)) && x" at the top of the empty document and asking "What does this do?".

Looking back, it was pretty silly but man did it really kill the confidence of 19 year-old me when it took me 10 minutes to work out that it detected numbers that were powers of 2. It really gave me a negative impression of Google's interview process (that and the complete radio silence afterwards), which I still think about when they send me their bi-annual recruiter emails. Funnily enough, the last email I got specifically mentioned that I had "done really well in the recruiting process in the past".