That's right.Monotheism is distinguished from henotheism, a religious system in which the believer worships one God without denying that others may worship different gods with equal validity, and monolatrism, the recognition of the existence of many gods but with the consistent worship of only one deity.
Source: Monotheism - Wikipedia
So why did you choose monotheism over henotheism (or any other polytheistic system)?
If you're a monotheist, then apparently you're okay with gods in general, so how do you justify believing that there are no gods beyond the first one?