Whenever you print anything large on the form1, it becomes especially important to angle your print in a way so that you minimize the size of the profile that is getting printed. Large profiles/slices create suction that can cause failures or if not, cause the lines that you see. Use the auto-orient button and position your model close to the hinge side of the peeling platform. If you can hollow the model before printing, even better.
Monger has some good advice. It looks like a delimitation problem to me where the model is under supported. If you continue to have trouble, make sure you message us at support@formlabs.com for assistance.