Right, I can see the blade now, thanks.
Just as loftyhermes says, the only way to check for blade "squareness" is with the blade in and fully tightened to the tension you would normally use. (Sorry, I don't know, but IF you're a 1st time scroll saw user, a good rule of thumb is to just tweek the blade and it should go "ping". Apparently it's supposed to be the middle C music note, but I'm not sure what that is ;-)!) Just go for a good "musical "ping", not a non-musical "thunk".
Now to your problem. It MAY be just the camera/lens/pic distortion, but from your pic, the table is well away from horizontal when compared with the background in your pic. But that does NOT matter, honest! What DOES matter is that with your credit card resting on the table, the blade is also well out of square - it's miles out, just as you say!
So what you do is simply adjust the angle of your table until it IS square to the blade. Just as you've done, measure it with your credit card, and keep doing it until the table/blade IS square, all the time making sure that the edge of your credit card stays flat on the cutting table.
If that means that your table ends up being not level in comparison with the room, that doesn't matter at all! The ONLY thing that matters is having a 90 degree angle between the table and the blade at the point where the blade goes through the hole in the table. That's all. Forget anything else.
If you want to do a double check against your credit card method then you cut half way into a block of wood, just as I (and someone else, I forget who, sorry) described in posts right at the start of this thread.
HTH