There are more reasons/exceptions as to why the result is anomalous. Some of these are variables, which can be controlled. We can control these, but not that accurately. But if we can control these, they should not make much of a difference. However, if combined they could. The concentration of alkaline is another variable that can be controlled. This is because the alkaline adds to the phenolphthalein, giving it a pink color. As we are using the acid to diffuse into the gelatine, the acid has to diffuse also/pas through the alkaline. If the alkaline is at a higher concentration, maybe it would be harder for the acid to diffuse. The alkaline is unchanged, so a weak acid [after diffusing into all the other cubes] diffusing into the gelatine plus the alkaline, may do so at a slower rate. This is a problem, which can be helped.
The temperature is also a variable. We did not measure the temperature or in any way changed it, instead we done the experiment at room temperature. The room temperature is not likely to change that much, but if it did it would affect the results. This is because the temperature is thermal energy, which when it comes in contact with the gelatine will change into kinetic energy. [If gelatine is colder than room temperature] This kinetic energy speeds the molecules up, which collide more then making the acid diffuse faster/at a greater rate.
Cube measuring is not a variable as such, but if wrongly measured it can obviously affect the experiment. We try to be accurate when measuring cubes, but no human can be exactly right. The reason there is an anomalous result could be any of the above, or some or even all of these exceptions combined. As there are reasons why we have a anomalous result, there are improvements which could eliminate any more anomalous results. For example, if we use fresh acid each time the pH of the acid would stay the same. This would be fairer, as the molecules in the acid would be the same speed, not some slower in other cubes.
As we would use fresh acid, we need the acid to come from the same place/ or have the same pH level. This is better, because if used different pH levels the actual acid would have different molecule levels. [More or less molecules in a fixed volume, which leads to either speeding or slowing, slowing if others are faster] Another improvement, which could eliminate anomalous results, would be to cut the gelatine from the same mould. This would make the pH level for all gelatine cubes the same, therefore having the same concentration. This would mean the cubes would be diffused at the same rate. Also if we place the beaker containing the gelatine cube and acid in a waterbath, we could control the temperature. We would measure the temperature of water using a thermometer, so all diffusions would be carried out at the same temperature. This would stop extra thermal energy [extra meaning room temperature higher than gelatine and acid] being transferred into kinetic energy, which would speed up the experiment. It would speed up the experiment because the molecules would collide more, diffusing at a greater rate.
All these improvements would not make that much of a difference, but we have a anomalous result so they are worth doing. We could investigate surface area to volume ratio at a deeper level.