Problem 1. Africa is enormous. There were some centralized Kingdoms on the Continent but they were usually hundreds/thousands of kilometers from each other. It isn't possible that they would be able to block Europeans from moving into the interior. Also, Africa has very few homogeneous areas that you could expect to fit a nation state in. So any surviving States would be Empires in their own right, as was the case in Asia. But the numerous local tribes are going to stuck between a rock and a hard place, either getting annexed by the a local Kingdom turned to a de-facto Empire or the Europeans.
Problem 2. It isn't possible to avoid some sort of European scramble after 1800. The scramble happened due to rivalries in Europe needing an outlet somewhere and the technological superiority of the Europeans over the local population. These factors can't be avoided. Plus Europeans are already on the continent by 1800, colonizing regions like South Africa or participating in the slave trade through trading ports on the coast. And it was actually the abolitionists in Europe and the British navy trying to abolish the slave trade and slavery in general that devastated the economies of the kingdoms, weakening them and putting them in a poor position to resist European direct colonial control later.
That said a "softer" Scramble is possible, and the odds get better the further back the POD is. It is certainly possible more states could survive. The Kongo Kingdom and Madagascar have a lot of potential, and of course there is Abyssinia. But you have to consider why and how they would do it. There is the Japan option, trying to industrialize and beat the Europeans at their own game, (this is very unlikely to work). Or the Siam option, playing European rivalries off each other to maintain Independence as a sort of "buffer" (which would require Europeans to have already occupied most of the continent as a prerequisite). Ethiopia, the only African State to survive the scramble did a little of both, they centralized, expanded a bit, had to defeat a European conquest attempt, and use the prestige from that to obtain international recognition as a Sovereign State.