This is why you need to do more riding by yourself. You need to see what you can do without the help and the security of the paceline. That will make you a stronger rider more than anything else. The paceline is great for spouting numbers but it gives you a false sense of what you can do. The last century I did this year(September) I was on schedule to finish in under 5 hours until I ruined a tire at 86 miles and had to abandon. This was on a 1972 10 speed(15 with the triple) touring bike that weighs 26lbs without supplies. In the rain with a 20 mile headwind. Uphill both ways in the snow.(kidding there) And I was getting passed almost as much as I was passing people. I was most pleased that I did a 22 mile stretch between rest stops in an hour(to the minute) during the heaviest rain after stopping twice to look at a map. But the point is I had no one to draft behind or protect me from the wind or to pull me along when I was tired.

That is why I think you are apprehensive about stepping out on your own.