My account has almost reached 10 payment submissions and I am still trying to test my form

Is there any way I can have more payment submissions so that I can test my form?

Since you are on the Free plan you only have 10 payment submissions. To have more payment submissions, you can either wait the first of next month for another 10, or upgrade to have 1000+ payment submissions - Pricing Page.

You can also get a few submissions for free by clicking some simple URL but, I'm not sure if they include payment submissions as well. To do that, go to Account > Get More and choose the option you want.