What you've just seen is why you should try more than one prop. Best thing to do with a new airplane is to figure on testing at least 3 props before picking one. Start with what you see at the field on your engine. Get that size and one the next diameter up. It's often worthwhile to get the same dia/pitch but in a different brand, especially if it looks a lot different. Different blade area can do wonders. Different tip shape is worth trying.

Say your engine is on a couple of models at your field, one turning an 11x6 and one a 12x5. Look at the planes those engines are on. Figure to try the prop that's on the model most like yours. Say it's the 11x6. When you're getting your 11x6, look at the 12" props and pickup a 12x5 or 12x6. If there aren't any, get a 10x8 or 11x7. Or just get another brand of 11x6.

See the plan? Try something, anything, that's close to what looks to be the best match.