Don’t confuse the ability to zip or button a garment closed with “a perfect fit”. There are loads of good books and online classes on fitting, and if you are a serious garment sewist it is great skill to add to your toolkit. Yes, it will take some time and some practice to improve, but in the long run your new knowledge will serve you well.
If you are interested in recommendations for resources, I especially like Sarah Veblen’s book titled The Complete Photo Guide to Perfect Fitting, and the online Craftsy class Sew the Perfect Fit. (Please note these links are affiliate links, and I will make a few pennies if you decide to purchase after clicking them! Thanks for your support!) There are loads of other options out there, and plenty of fitting systems. Experiment, try out as many as you have the time, money, or energy for, and decide for yourself what system works best for you.
What fitting systems or resources do you like? Is getting a good fit hard for you? Do you love the challenge of figuring out how to get a great fit? I’d LOVE to hear more from you!!