This mismatch is a potential problem to the cell, because it represents a potential mutation. DNA molecules will be mutant. Although the mismatch produces some distortion of the DNA double helix, that distortion by itself does not generate a problem. The distortion will not impede either RNA polymerase or DNA polymerase, because both polymerases unwind the DNA double helix as they proceed. Note that, even though this mismatch can be converted to a mutation by replication, the mutation may not be harmful.
Many mutations have no detectable phenotypic effect.
Also, please note that mismatches do not necessarily arise as a consequence of replication errors. Unless one knows what the original DNA sequence was, there's no way to tell for sure which base is correct. List all of the repair pathways you can think of that are capable of repairing a situation where T is in one strand and G is in the complementary strand. They do so by removing one of the mismatched bases and replacing it with the correct complement to the other base.