Hi Al,
You obviously had a teacher who didn't believe much in giving encouragement.
What I think is this. The hell with the person who wrote that. If you are at an age when you want to do it and you think you have something to say, just relax, go ahead and do it. If good grammar were a prerequisite to writing a blog, most of them would immediately disappear.
If you want us to review a paragraph here and there for you, we'd be happy to try to help. Just post it, in the Writing Section of the Forum. I don't know much about grammar checkers. I'd guess that the one that comes with MSWord is probably as good as any.
Good luck, have fun!
Clive