Can I control how fast my sewing machine goes?

Three ways, and the first is free.

The pedal is proportional. Most people press it like a switch. It is not — light pressure gives a genuine crawl on almost every domestic machine. Practise sewing a line at the slowest speed the pedal will give you; it is a learnable skill and it is the single biggest control improvement available.

A speed limiter, on most computerised machines. A slider that caps the maximum regardless of how hard the pedal is pressed. Set it to half and the pedal still works normally within that range. This is the right answer for a child learning, and for anyone doing fiddly work.

A start/stop button, on some computerised machines. Runs the machine without the pedal, at a speed you set. Useful for long straight seams and for anyone who finds pedal control difficult.

And the handwheel for the last few stitches over something thick. Turning it by hand is not a failure; it is what experienced sewers do at a jean hem.

If your machine only runs fast, check the pedal is not sticking and that there is no fabric or cable pressing on it. Otherwise it may simply be a machine with a coarse pedal, which is common at the bottom of the market.