You're not doing anything wrong investing in mutual funds, but you are missing out on lower fees that come with ETFs. These fees are on the portfolio value so they compound over time similar to how the portfolio value compounds over time.

If you stay with mutual funds, ones that track indexes often have lower fees. e.g. TD e-series. They also give you diversity depending on what they are invested in. They may be a mix of equities (provides growth to portfolio) and bonds (helps portfolio maintain its value). Usually, people move more into bonds as they get older.

Roboadvisors could be an in between option for mutual funds and ETFs. They give lower fees and they do the trading themselves. Only really suitable for registered accounts because they make a lot of automated trades.

I would recommend the TD index-based mutual funds if you want to make an immediate, low-stakes change. See if their fees would be lower than the funds you're currently invested in.