Scale is not the right tool for the job at hand. You need the faces of the base to be wider than their top counterparts. Scaling will make the base larger but won’t make the base wider the way you need it to be.
This shows the base of the crab scaled up.
In section you can see that the inner walls lean the wrong way. This would make a very weak stamp for leather work. The stamp would be brittle and likely shatter.
Instead make the base wider using Offset, Move the inner curves upward and connect them. Curviloft by Fredo might be a good choice for connecting the edges.
No matter what, you’ll need to work at a much larger scale.Either scale the model up while it is flat or use the Dave Method.