It's perfectly normal to not be satisfied with the first results of a costume you make. With some costumes, I'm never done working on them. Others take a few tries to get it right. Each time you work on a project, you learn new techniques and refine your skills. Sometimes taking another shot at an older costume can be very satisfying!
With a character like Saber, I'm often motivated to revisit older costumes I've made and improve them. Taking her armor-less blue dress for example, the first time I made it was in 2010. I was working with a very pretty upholstery fabric. I loved the color and sheen, but the fabric had no give whatsoever.
After I commissioned GS Props for my Caliburn in 2013, I decided to give the costume another shot with fabric that matched my prop's paint. Using a stretch satin and making a few alterations to the same pattern I drafted in 2010, I remade the outer blue dress. The fit was instantly better! I also remade the top of the white dress, creating a higher cut to de-emphasize my chest. I kept the embroidered parts of the white dress because they were my favorite part of the first costume.
I debuted this cosplay remake at Anime Conji in 2013 and it was featured in Cosmode after shooting with the staff of the magazine at the event! I've been a reader of Cosmode for many years, so I was excited and humbled to show off several years of work and growth with this costume in a publication I'm a fan of.
It's okay to not be satisfied with your work. Don't let that discourage you from trying again. Most of all, don't let others make you feel like you have to be perfect! There is no such thing as perfection. Cosplay is a challenge and a learning experience, but above all else, it is a hobby meant to be enjoyed. I'll never be a perfect costumer, but that's really not a bad thing! It gives me something to work towards and feel proud of when I achieve goals.