Checking oil level with bumper rail level

I'm still finding the oil check to be a challenge.

I figured that if my hull is level, then the engine oil level should be level. I'm all set with that. But, after I ran started and ran the engine for 90 seconds, waited 30 seconds and checked the oil in the driveway, it read over 1/2 inch under the minimum. I called the dealer that I bought the Spark from. They said to go out on the water and run it for at least 10 minutes (they said that if it was really low, an warning indicator would go off). So, I went out on the water. The oil rose to just under the minimum mark. I added 4 ounces. Then it was just over the minimum mark.

Two days later, I went out on the Bay again. I ran it for more than 10 minutes and checked the oil. It was back down just under the minimum mark again. I put 4 more ounces in. I ran the engine and checked it again. It was just over the minimum line. The oil is clean and now I only have 10 hours on the ski. Anyone have any ideas on the oil level? Maybe the dealer didn't put enough oil in it. I'd hate to think that's its burning that much oil.

Also, when is everyone doing their first oil change? The manual says 50 hours. My local dealer (who wanted me to pay full sticker price for everything and so I didn't buy it there) says to change it at 10 hours.