Ask yourself as you look at the color you want to replace...."can it be darker?"
One reason you may not like this purple is because all your fabrics are in the MEDIUM value range; this is not a fault, it's very common to beginning quilters *and* many long timers.
Most blocks/quilts have better visual appeal if they have more CONTRAST between the colors chosen. Practice "seeing" this truth by playing around with the fabrics you DO have, and with other colorful objects - even paint chips!
Pick a color (try red maybe), then in the reds chose a LIGHT (baby pink, right?), a MEDIUM (true red?), then a DARK (how about burgundy/rust?).
Notice how contrasting they are to each other.
Notice how they affect the value of the fabric placed next to them when they are paired together.
To take it further, try placing a value between each of the three so that you have a 5-step color study. Practice this trick when you fabric shop, or even just do it for training without making purchases for a while.
Personally, when I look at your theme fabric I see a dark blue calling.
You're doing great, keep at it!
Jan in VA