Don't put it in a bowl. It's still small, right? Good. It's fine for now. But yes, return it. For otos you should really have 4 or so in a group so they feel safe. YES they are alright with bettas, but some bettas can be mean. I watch mine stalk the poor siamese algae eater
I have a SIAMESE algae eater. It is MUCH smaller than the CHINESE algae eater and not as aggressive apparently. Avoid plecos, obviously, as I have one that is 8 inches or so big and sticking that in a 10 gallon?! No. They grow big FAST
The chinese algae eater will out grow the tank and yes cn hurt or kill your betta. You could find a siamese algae eater but a warning... they are profficent cleaners. they clean and clean and CLEAN!!!
I do not have a speck of algae in my tanks because he finishes within days - so make sure to get algae wafers, and even some cucumber now and then if you did get one.
OTOS should have hiding spaces, and lots of plants/ornaments to hide under and behind. They can be skittish! Usually a sand substrate is best for them, but gravel is "alright".