Welcome aboard! Your coastlines look nice, I think they're fine as is. The whole set of them, though, looks a bit like they're crammed into the available space (I can almost see the callout boxes like they're close-ups or insets). If it were my map, I'd keep the biggest continent and remove all but one or two of the smaller ones. Also, you may want to either fill in or open up to the ocean the large inland sea; all that water wants to drain. All in all, great start, can't wait to see where it goes.