Yeah, 50 degrees is probably going to be too cold for that yeast. Lager yeast do well at that temp though, but even so you need a lot of yeast - perhaps 4-6 vials/packs or a couple packs of dry lager yeast.
I recommend warming the beer up to the mid to low 60s, but don't let it get too warm. Fermentation temps much over 70 degrees can generate some unwanted flavors. And remember that fermentation is exothermic so your fermentation temp could be 6-8 degrees over ambient.
As long as your sanitation was good the beer should be fine, especially at 50 degrees.
Also, you may way to pitch more yeast, especially if you used liquid yeast and only pitched one pack/vial. If you are new to brewing I would recommend starting out with dry yeast until you get the hang of making yeast starters or pitch multiple packs/vials.
Good luck on your beer!