"Transit (C) visas are nonimmigrant visas for persons traveling in
immediate and continuous transit through the United States enroute to
another country"
"A foreign citizen whose layover in the United States is for a primary
purpose other than to transit, for example to visit friends or
sightsee, requires a visitor (B) visa."
Ref: http://travel.state.gov/content/visas/english/other/transit.html
Essentially I believe this would come down to convincing the immigration official that your visit to your uncle was purely incidental to your transit. You could have problems if, for example, you could have got an earlier flight out of the US without visiting your uncle.
On the other hand, if it looks like your stay in the US wasn't longer than it needed to be they probably (probably!) won't mind where you go during that time.