You are always expected to estimate task durations. It is especially hard to do for development tasks. You get better in time but game projects frequently put you into unfamiliar territory.
Add realistic error
Unfortunately, how much error is realistic depends on many factors. If you actually need to retrieve that information from a blog post, we can safely say it is more than 2x in your case.
Say, your initial estimation is one month. If you have done it before, stick to your estimation. Otherwise, 2 months.
Estimation was 3 months. Your performance will consistently decrease. If you are experienced, expect two weeks delay. Otherwise, 8-9 months, there is no way an inexperienced developer can plan 3 months of work accurately.
Now, those were only for single person tasks.
Let’s say it is the first task of your newly formed team and you are the fresh, inexperienced lead. Your initial estimation was 4 months and you completely overlooked the upcoming storming stage. Everyone seems bright and get along really well, after all.
Now when it begins, you don’t want to be out in the open. So what you do is, you get behind the junior artist, as the Wacom displays are expensive, nobody will dare throw things at you.
The project will likely end up in development hell, and get cancelled, but not before everybody hated you. Bottom line is, always take stages of team development and decrease in performance into account.
Don’t stare into the abyss
You realized you don’t know how to do X. It is OK. Don’t stress over it. The unknown seems so hard it makes everything else look simpler. They are not simpler. Don’t let fuzzy parts of the task completely drive your estimation.
Visualize the steps
Don’t just outline the task and focus on the duration of each bullet. Visualize the complete pipeline instead. For a second, be overwhelmed by the amount of minor labor and glueing needed to complete it.
Reorganize the task
Don’t worry. Your estimations will get better. But that is mainly because with experience, you learn how to reorganize and regroup the tasks in ways that makes them more meaningful from a task management point-of-view.