To be very clear:
It might be a problem caused by using a free subdomain, but I have no idea if that’s really the issue. I also cannot make any guarantees that using a different domain name will help.
Again, if you want to be sure why some other website says your website is harmful, go to the website where it says your website is harmful and start looking for solutions from there. We do not operate Scam Adviser, and we don’t know why your website is listed, let alone have the power do so something about it.
Not using a free subdomain may help. But I cannot provide any guarantees that it will even help solve the problem a tiny bit.
Just buy a domain name at a domain name provider of your choice and add it to your account:
Please note that your website being listed at Scam Adviser says nothing about it’s position in search results. Maybe the search engine also thinks your website is dangerous, and maybe not using a free subdomain may help with that. But again, zero guarantees.