Girls should i tell my gf this?

I'd first recommend u discuss the experience with her. How much did she enjoy it? Then ask if she'd like to do it again sometime because you enjoyed spending time with her. That way you don't have to mention you enjoyed it and like preserve your manliness. But in all honesty I see no reason why you can't just tell her. If she cares about u she won't change her mindset towards u over such a silly lil thing like dat but best to keep it between u two for obvious reasons xD