I have started Scanning a website and it is scanning it since  last 24 hours and still hasn't completed. When I stop it, I have to start it again.

Can you please tell me if I have to stop scanning in the middle and generate sitemap till that point how can I do that?

At the moment when I stop, it again ask me to start scanning.

It is taking ages to scan my small website.

Please help

So I took a short test scan, and all the URLs there look correct.

Incase you believe any URLs are wrong, you can try exclude them using exclusions in output filters and analysis filters.

If you find all the URLs found by A1 Sitemap Generator are correct, then that is not the problem.

...

In that case, you will want to configure your webserver / website / A1 Sitemap Generator for higher speed. See:
http://www.microsystools.com/products/sitemap-generator/help/sitemap-generator-resume-scan/

(for reference, A1SG is configured to about ~5-10% of max speed in default settings. The reason it is preconfigured that way is that that some webservers/websites can not handle higher load.)