Then here's what I'd do.
Let the starter go for two days then put it in the fridge for two. Then carefully pour off the liquid being careful not do disturb the yeast in the bottom. and boil another 2L of starter and chill to fermentation temp. Add that to the yeast and let it go for two days again. At that point I'd be willing to bet you'd have enough cells for your 1.046.
There's a general rule that the count will double every day (roughly and I may be off) depending on oxygen and temp. Swirl the starter often to increase o2 exposure.
What kind of beer?