People who can sew. Please help me think out dog bed plan.

[ThatDirection]

Help. I've bitten off more than I can chew and attempted to make a dog bed. I've got a rectangle of memory foam. I've gpr fabric. So far I've made a top and attached sides. I had planned to have the fastening on the bottom, and to add velcro to do it up. I can't work out how to configure it. I don't have a zip. Can I salvage this with velcro or any other ideas? I'm about to throw the whole thing in the bin.

Why not do without a fastening and make an envelope style opening instead

Would that be better placed in the middle of the bottom? So, to clarify, split the bottom in two (allow hems for both pieces) and attach the edges to the sides of my dog bed, slightly overlap the 2 pieces where the opening is?

yes exactly that

If you have an overlap, you can add the Velcro to that to hold it closed.