Based on my knowledge you only need to prove basic language skills/comprehension.
You need to be able to successfully establish your self-employed business in Canada which requires enough English skills to effectively communicate & comprehend the language.
A 4.5 score demonstrates a basic level and a good foundation for further development. Also one of the new arrival services is language testing and assistance to enroll in classes. There are also slightly lower requirements for individuals with English as a second language. From research I did a minimum score of 4 is required for most PR programs -
https://ielts.idp.com/canada/prepare/article-what-is-the-minimum-ielts-score-to-get-canada-pr-and-work-there
Based on your written communication here & score of 6 for speaking it seems you just need to work on your comprehension (reading/listening) and you’ll be just fine. Being in a largely english speaking country and using the language daily will soon improve your skills greatly. In this category it’s at the officers discretion but it sounds like you’ve met the minimum requirements & exceeded them for speaking/writing which seem to be the most important for your NOC.
If you’re worried - You could consider including a letter of explanation stating that you will enroll in an English language course/work on your skills in the coming months (even better if you can provide proof). And how you had limited time to prepare for the IELTs but are very passionate about this opportunity to move to Canada and willing to put in the extra work to ensure you are able to adapt smoothly and make a strong contribution to Canadian culture.
I hope this helps! Good luck