If your matzos are broken a little bit around the sides, they are still regarded as sheleiemim for lechem mishnah, according to the Chelkas Yaakov (92). The reason that we need lechem mishnah is because we need a challah that is choshuv and a challah that is missing a small piece does not lose its chashivus.
Although there are some Acharonim who are machmir, since the mitzvah of lechem mishnah is only Miderabanan, one can be lenient in this regard.
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