Wearing my retainer again after two years. Any suggestions?

I had braces for two years in grade 10-12, it's been about 2 and a half years now. I wore my retainer for the first 6 months. My bottom teeth have slight gaps between them now - even though I do have a permanent metal brace at the back and my bite feels slightly off. My top retainer fits slightly, but my bottom does not fit at all. Will I need to go get a new retainer to fix this issue, and can I wear my top retainer still? I thought the point of have a permanent metal retainer was to help prevent this?

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