If your batch was 5 gallons of 1.082 and your starter was 2 liters (Just a bit over a half gallon) of 1.030, then at worst you would end up with around 5 1/2 gallons of something like 1.077 (not much under your target and way different from the 1.062). Just go with your gravity reading from before you pitched.
Even without a stir plate you can make healthy starters and decant off the liquid. Before I built a stir plate I would make a starter and keep it in the living room on the coffee table--and not just as a conversation starter. While watching TV, reading, etc. I would reach over every hour or two and give it a good swirl to draw in air. Anytime I passed through the room, I would do the same. Do it again before bed and then as soon as I got up. Once again before heading out the door for the day and then another swirl as soon as I got home. This isn't as good as sitting it on a plate with a steady stream of oxygen, but it works fine. Having it where it is visible helps to remember to keep swirling it. There are no hops in a starter so no worries about it getting skunked. The day before you are going to pitch, refrigerate it overnight. On brew day decant much of the liquid, then let it sit out warming to ambient while you are brewing. When your ready to pitch, it's ready to be pitched.
