A small difference in the group sizes won’t affect the results. Researchers have a way to mathematically figure this out. Too many patients in one group compared to the other could make a difference. The total number of people in the study is also important. The larger the number, the more everyone in the population is represented.
Many researchers begin with a small sample as the pilot project. Once the study has been finished, a second, larger study is often done. This confirms the results of the first study and offers a broader group to sample.