At the end?

Yes. Ann and Anne are both correct spellings, Anne probably more actively used.

Mary Ann, Mary Anne. Both fine.

Thank you :) Is it more common as Maryanne or Mary Anne?

Sure can!

I think the e at the end looks prettier for some reason

Normally I see people using a - in the middle.

Mary-Anne but honestly double first names aren't common around here so I am not entirely sure.

Probably. I don't see why not, it's not like it's an illogical spelling, it's just two names tacked together so both Ann and Anne make 'sense'.