I think I found your problem.
Try this cycle: - Add however many cards you like - Study - Got bored and didn't finish all your cards? Stop and don't add any new card until you can finish quick enough to not get bored - Finishing quickly? Add more cards
The exponentially increasing interval is your friend. Before you notice you won't be studying more than 10 cards a day :)
It doesn't feel like it in the first ~10 days of a block of cards, but there's a jitter in the spacing function, so you will see the same block at the same time 2 or 3 times but then they'll start dispersing and be a lot less overwhelming.
And most important of all: don't be afraid of slow progress: progress is progress!