Hey man,
I don't think indicating interest to a girl is mushy or will affect your manliness in her eyes. On the contrary, it might actually show her that you have balls and you go for what you want in life. This is definitely sexy to a woman.
The reason she says those things when you get mushy is probably a way for her to test you. If you are all manly in front of her, she might be testing you to see if you really are what you show to be.
Hence, you being mushy and her pointing it out shouldn't bother you, if you really like being mushy at times. There is nothing wrong with being a strong man who has a soft side. Hiding that soft side makes a strong man look weak though. Embrace it.
As far as telling her you like her. Be 100% honest about the way you feel about her. Don't worry about being rejected. Not going for it and hoping her to take the lead might not take the relationship anywhere, anyway.
Check out these articles. Should get you motivated: This one
http://www.pickupevolution.com/ratisse-inner-game/ and this one:
http://www.pickupevolution.com/legend-e ... -blow-out/
All the best