I think most of us have made mistakes. It is probably a part of the learning curve. As far as your concern about the speed others work at, don't worry about speed. #1 This is a hobby, work at a comfortable pace that allows you the most enjoyment of the hobby without putting extra stress or pressure on yourself. #2 We have people of all ages on this forum. Some are retired and can make their railroad a full time pursuit if they want to. Others are still working full time and have less time to devote to the hobby, and still others are having to work full time plus overtime. #3 Some people are able to work at a faster pace than others and still turn out good work.
As an illustration, a friend of mine is a general contractor, and I hired him to remodel my house. He is very meticulous, but that results in the work progressing slower than would be ideal. He has apologized for taking so long, but I have watched "Holms On Homes" on the Discovery Home channel, and the more I see of the night mares he deals with the better I like the slow meticulous way my friend works. As an example, he added on 4 feet to my dining room. The new sub floor is "dead on" plum in every direction. He installed a new floating floor over the sub floor and expected to install the new floor in 1 day start to finish. He noticed as he was checking out the old sub floor that there was 1 board running across the floor that was about 1/2 inch high. He removed that board and found that he had to install a thinner board in it's place and then run the sander over it to thin it a bit more. After that was done, he checked the floor and found another area that was 1/2 inch low. He ended up using spackle to build up the low spots and had to let it dry before he could put down the plastic moisture barrier. The result was that he ended up spending 3 days to do what he thought he could finish in one day. However, the new floor is dead on flat in every direction and absolutely free of any squeeks. I would trade a couple of days for quality anytime.
What I'm trying to say to you in a very long winded fashion is work at a pace that is comfortable for you. Don't worry about how long it takes to finish or even how long it takes to get trains running. Expect to make a few mistakes and need to tear things out and redo them. When model railroading ceases to be fun, take time out to do something else and then come back to it. Any time you run into what seems like an insurmountable problem, come to the gauge and ask questions. Over the years that I have been here I haven't seen any one ask a question that didn't receive a bunch of answers with one or more ways to fix the problem!