Not sure what you mean by "it won't let me send with my number using iMessage"?
Again, that is how it looks normally:

The first number you see listed above is the number of the iPhone that iMessages is set up on. The second number is another iPhone number that I manually entered.
You can see that the first number is greyed out (as it should be).
Does your number have a check mark next to it?
If not, then that is the issue, not that it is greyed out.
If the number does not have a check mark next to it, then sign out of iMessage by clicking on your Apple ID at the top of the screen under Settings>iMessages, and then sign back in again. Do the same with FaceTime if that is the issue there.
Cheers,
GB