you were driving at 3.75 miles per hour according to yourself

People generally drive more than 60 miles per hour on highway.  Even assuming you were driving at 40 miles per hours (minimum legal speed genearlly), 1 minute means 1,066 meters.  

Why do you think you had your left turn signal on for 1-2 minutes?  It cannot any further from the facts because for you to have had your signal on for 1 minute, to cover 100 meters, you would have been driving at 6,000 meters per hour, i.e., 3.75 miles per hour.

You did not check your blind spot.  100 your fault.