Homebrewing - My Schwarzbier

Well, it's been about two weeks since I made my first beer in about two and half years. My Schwarzbier (Black Lager) has been fermenting in the fridge. It started with an original gravity of 1.042 and is currently at 1.020. I missed the target gravity of 1.052, which has always been a problem in my brewing. My OG has always been lower than what it should be and I'm not really sure what I may be doing wrong. It could be as simple of not boiling it long enough, as I only do it for about an hour.

I took a sample last night, to get the 1.020 gravity reading, and the beer tastes pretty good. If you will remember, the kit I used was about a year old. I'm pleased with the taste so far. I may try to swirl the carboy a little bit, being careful not to get too much oxygen into the beer, as it will cause problems. I just need to the gravity to drop some more before transferring it to secondary fermentation.

So far so good, though.