sounds like a good learning experience
it's been mentioned to monitor riders in front of you, but I like to place myself where I can 'see' 3-4 ahead, at least. 'Learning' the gap distance between riders is important. Experience lets you develop an understanding of the visual distance between you and other riders - I like to use the head and shoulders. That allows you to 'see' ahead quite a bit and anticipate much better.
You can 'practice' this observational skill during slower warmup times, when riding is steady. Place your wheel the distance you wish from the rider in front, then look up to observe the distance - try to hold that distance. AT first it will take some concentration, but surprisingly quickly it'll become second nature, as does constant scanning of the surroundings. Soon you won;t even notice you;re making adjustments to your position based on this observing.
Additionally, unless there is a single paceline under high duress, I never ride directly behind the rider in front. I offset a few inches to one side. It allows for some natural accordianing of the group without causing disasters. Additionally, you'll easily be able to 'see' 3,4 or 5 layers ahead to anticipate much better, and you have the ability to see some road hazards. When you see a road hazard hand signal, that's the time fall in line with the wheel in front (hoping the rider in front is picking a good line...)
I try not to offset to the 'outside' of a rider unless I plan on advancing my position. If riders in front are 2 or more abreast, natural quick movements go to the outside. It almost never happens that riders abreast go towards each other (except in a crazy sprint...); so the safe place to be is between 'pairs'/3/4 upfront when in a large group - you have a guaranteed 3 ft of space between them that will keep your wheel clear.
As in here:

each following rider is offset from the pair infront...
However, when the group is riding 2up in steady tempo, it's expected that you'll also follow suit and ride behind the wheel in front, and not hog the middle...
...lot to learn, but riding in a fast group is huge fun!