Assalamu alaikum wa rehmatullahi wa barakatuh
And it is He who spread the earth and placed therein firmly set mountains and rivers; and from all of the fruits He made therein two mates; He causes the night to cover the day. Indeed in that are signs for a people who give thought.(13:3)
It is not the concept of whole flattened Earth,but the different landforms are mentioned.
The spreading of the Earth as bed simply means the creation of plains for our convenience.
[He] who made for you the earth a bed [spread out] and the sky a ceiling and sent down from the sky, rain and brought forth thereby fruits as provision for you. So do not attribute to Allah equals while you know [that there is nothing similar to Him].(2:22)
See the definition of plain:
A plain is a broad area of relatively flat land. Plains are one of the major landforms, or types of land, on Earth. They cover more than one-third of the world’s land area. Plains exist on every continent.