There is something off about all this. Never mind about the wrongs or rights of an early scan.
You want a scan that costs a few quid - less than the cost of a meal out.
You say your partner is stingy and doesn't want to pay for it. Then later you say that you would pay for it, and that you also paid for the meal that you think he is putting more importance on than the scan.
So, YOU paid for the all important meal, and he didn't pay for anything. So what are you actually talking about here?
You say My husband doesn't want to pay for an early scan.
If you actually, truthfully have to get his permission to spend £55 of your own money, then something is very wrong here, isn't it?
If you are upset that he doesn't happen to agree with you that a scan is necessary, then that has nothing to do with the actual money side at all. But what you say is: My husband doesn't want to pay for an early scan.
Are you being financially abused OP? Because if you are, if you cannot spend your own money as you see fit, without 'permission', then please be very careful because this sort of controlling behaviour will only get worse now that you are pregnant. He won't magically get better just because he is going to have a child, he will likely get worse- statistically, abusive behaviour ramps up when a woman is pregnant.
You will be on Maternity Leave soon enough. Have you discussed with him that you will need shared access to all family funds during that time? Or are you hoping he will be understanding and suddenly stop being stingy?