I'm not sure.. but still a suggestion
Set up your blogger custom domain to .com or any other paid domain (mywebsite.com)
Now try redirecting your mywebiste.tk domain to mywebsite.com.( 301 redirect ) so you don't loose your existing users. If possible, mention on your website that you have moved to a new domain so you don't loose the direct hits.
And mention both the domain in your Google Analytics account with (mywebsite.com) as primary and others secondary so Google knows that both goes to same and which domain is primary.Hope that would do.