it sounds you were too slow but merged so fast. giving the left turn signal does not mean you get the right to change lane automatically, and 1 / 2 min blinking totally confused the other driver, will you chang lane or not?
it sounds that care was in your blind spot, did you turn your head ?
Normally, I will watch the space clean, follow the traffic, and give the signal for 5-10 secs, then start changing lane gradually (not drving slowly). However, sometime, you need change lane fast, especially in rush hours or in an area with many agressive drivers.
