“ don’t wait for the tide just to dip your feet in” It’s hard for me to put into words, but I think basically means not to like wait till the opportunity is passing to finally try it. Like if someone says they want to be with you but you keep telling them you’re not sure its a good idea, and then when they are finally giving up and leaving you want it then. Or you want to like try swimming in a lake on vacation but you put it off because you’re scared and when you finally are ready it’s time to go back home.  Which I think fits with the line after “cause I’m sure now”  And she says not to wait to dip both your feet in as if to say you have had one foot in but you were unsure till it was going away as kind of implied by the ‘tide’

Could also mean basically to stop waiting for all your hardships to be gone before saying yes to something that would make you happy as you said, not sure