SANIBEL ISLAND??????

My friend and I and our moms are going down to Sanibel Island for her 16th birthday at the end of april. We are staying at the Marriott Harbor Resort and Spa (I dont remember the name) but when I was looking it seemed like it was kinda boring I guess..and the water not that nice because its a harbour i guess. So is it far from a good beach that has like blue water and is there anything fun to do like at the hotel so me and my friend can "party" without having to be with our moms the whole time (we wouldnt be allowed to venture off alone.) And what are some fun things that we can do there. Ive read about finding seashells or taking a nature hike thingy but anything that is really exciting i guess. O and any nicer restaurants........THANKS to any answers!