Chance to get no 6* in one pull: .995
Chance to get no 6* in 11 pulls: .995^11 = 0.94635457981

Chance to get one or more 6* in an 11 pull: 1 - .995^11 = 0.05364542018

So you have just above 1 in 20 odds (5.36%) to get at least one 6* in an 11 pull on the gacha.