Just think about this. You've asked do you have a moment of doubt (about what?) or a bad day after manifesting your desires. Everybody has a moment of doubt about all sorts of things, it's normal. I had more than a moment of doubt about the interview for this job I have "I am sure they will want someone better than me" but they didn't and I was offered it. 

I wanted a car, similar to the one I had to scrap. I got almost an identical one, so I manifested it, and quite quickly too. It is sitting outside my house, and I have had a few "bad days" since then when things haven't gone right, for example, it has rained all day today and I forgot my umbrella, the bus sailed past and didn't stop (I don't take the car to work) and it made me late, things like that. Does that mean I have to start all over again, or someone will steal my car, it will be in an accident, or something?

Is that what you are asking? Because I think you are worrying too much if so.
 

Don't worry too much about it. We are humans, we have our moments, and that's okay. I know that some LOA teachers make it seem that in order to manifest, we always have to be in this 'manically happy' state - but that's humanly not possible, lol. What really matters is your overall vibration, what is dominant. If you're at least 51% positive, you're good to go. Also, the seed of your desire has been planted, it's already growing, so a negative thought won't kill it off, the order won't be cancelled. Just don't stress about it too much, focus on being positive overall.