That kit is pretty good- I made it last year when I wanted an Oktoberfest and didn't have alot of time.
I wouldn't worry about the original sg- since it's extract, there is no way to miss the sg. The sugars are in there, but maybe not thoroughly mixed up. Sometimes when you top up with cool water, even though you stir it doesn't mix up totally and the heavier extract sinks so that the sample you take from the top is lighter. It doesn't matter, since the yeast will find the sugars and that will mix it up!
Your blow off tube sounds fine. I'd put some sanitizer in the container, just in case.