You don't list any processing software and I am not familiar with QHY Capture but if it is like most other capture apps it has little or no processing functions.
You have just enough integration time to naturally resolve some of the colors available in M51, but the color you have is not the predominant OSC color in the object. The key to knowing that is the fact that your background is the same color as the object and the entire object is that one color without any tonal variation between the light areas and dark areas in M51. This is called color cast.
I think you are making a mistake by believing that dark magenta is the natural color you get for this target with your new camera and
@Arun H. is absolutely correct advising you to search the best OSC images of M51 to see the colors and look at the technical cards to see what others are using to process those colors. Almost every processing program will allow you to manipulate a multitude of parameters including brightness which this image also needs.
Most around here will also advise you to acquire and learn to use a dedicated Astro imaging program such as Pixinsight or Astro Pixel Processor.
Unfortunately there are no shortcuts in this hobby and imaging and processing skills take a lot of practice.
Specifics,
Always as much integration as you can get
Yes more color and tonal variations of colors including color luminance.
Your image has NO color balance
I suspect you already know your guiding is good re: 10 minute subs
Do you really think your stars are too big?
I have no idea what a flatter background means, start by losing the color cast
Good Luck
scott
Here is an more or less average M51, there are many many more...

M51 Wide, OSC