How to not misspeak

Try to avoid one word answers. Let your answers come with a very complete explanation. So, “did the doctor get back to you” gets an answer like "they got back to me yesterday afternoon, and I made an appointment".
Including an explanation in the answer prevents you from making up a simple one-word lie which, in turn, makes you think more carefully about your answers before you give them.

I've never encountered anyone with this problem before.
Maybe it's a neurological quirk; I don't know.
Might be worth seeing a doctor for a check with a psychiatrist.

Check with yourself whether the lie is something you wish were true.
In which case, perhaps it's a form of impulsiveness. That can be neurological and there are things that can be done about it.

Check with yourself whether your answer has an element of ego in it, hoping others will see you in a better light.
If so, the lies will eventually bring you undone when people realise you talk bullshit, or worse, are not honest.

If it turns out to be not neurological, then you should be able to change it yourself. Slow down the time it takes to answer a question. Think of the truth and then say it. You might be surprised how warmly be respond to the truth.
For most people, even an unpleasant truth (said tactfully and with empathy) is preferable to a pleasant lie.

Do you want to know the absolute cure for this? It takes courage but I'm not recommending something I don't do. I began to do this long ago and I don't misspeak ever.
Every time you say something that isn't true, go back to that person and admit it and apologise. It also takes courage then when someone asks you a question about doing laundry and you have to admit you didn't - but it's better than coming back later and admitting you lied. The unexpected thing that happens is - people respect you for doing so. It soon cures you. I don't know anyone who hasn't been dishonest at some point - we all understand it.
I'm 100% genuine about this. This is the way I live.

Do you lie about lots of things often? Like important things

It might be a habit acquired from your childhood. Maybe you had to lie to a parent to avoid bad consequences.
Try to make a habit of telling the truth perhaps ?

I don’t lie.. I withhold key information

Pathological liar?

Bipolar?

It's a psychological habit called compulsive lying. If you're like me then you used to consciously lie to people which started it for you. It's easy to solve it. Every time you say something to a person you think "Was that a lie?", and if it was then you tell them that you said the wrong thing and that you meant the other thing (the other thing being the truth). Just doing this a few times will teach yourself that the consequences for telling the truth isn't bad, and thereby defeat the purpose of lying.