I'll be willing to stipulate your 7M Muslims in the US, I'll even spot you another 500K to make the math easier.
OK, 7.5M out of 300M (your number for total population of the US) is, anyone? 2.5%
While there may be a large number of individuals, the overall proportion is small.
To further illustrate, if China had 30M Muslims, where would that put them on the list of nations with most Muslim residents? I'm guessing around the top 10. That would also be 2.5% of their population. Based on that, would you call China a Muslim nation?