If you think it is too high only buy a small amount with a plan to buy more if it goes lower. This way you will at least have some if it goes higher.
This seems a good idea, and in fact I use to do it. For example, if I want to start buying ethereum but the price seems too high, I start by buying a fraction of what I am willing to spend. If I have $200 to buy Eth, I only buy $20 expecting a better price to buy more, but if instead of lowering the price keeps going up, I keep buying minimum but consistent amounts.