Glad you're okay, I never leave the flow of traffic for exactly this reason. I may be in the bike lane but I move around within it and I take the painted line frequently. I don't like the idea that cars, trucks, or buses can use the excuse that a bike lane is a "penalty box". In my opinion, if I need to use "their" lane, I'm entitled to take it in a safe manner.
You made a mistake by reacting too slowly to the threat. Your glance over the shoulder came too late. If you could have taken a place outside the bike lane you would have missed the shopping cart. If you weren't able to take a place in the vehicle lane, you should have been on the brakes and had time to stop.
Yes, hindsight is 20:20. But if you don't ask yourself, "What could I have done differently?", you may not get the benefit of learning from the mistake.
BTW: If riding like I describe sounds like an invitation to driver rage, I'm guilty as charged. I've got no sympathy for those that would use the size of their vehicle to establish their right to the the road. OTOH, it has taken me a long time to accept that I should wait in a line of traffic instead of barreling to the front. I hope that makes up for my impertinence.