8 months is not late at all for crawling. My DD is a week shy of one year old and only does a half assed commando crawl, and out of my mother group only 2 babies are 'proper' crawling and only one is walking. BTW she loved tummy time and first rolled at about 4 weeks, so you see huge variations on development milestones which are all OK.
I know it is hard not to worry but on this one it really isn't time for concern, and it won't be time for concern for quite awhile yet.