Watch app will not let me sign in with my Apple ID

Is this a new watch or did you buy it second hand? If it is not new, it is probably Activation Locked which is an anti-theft feature that cannot be bypassed. Only the previous owner can remove the lock and Apple will not help you find that owner. If the previous owner cannot or will not remove the lock then the watch is useless to you or anyone else. Dispose of the watch properly or try to get a refund.

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support

If you are the ORIGINAL owner, then see:

How to remove Activation Lock - Apple Support