A gauge isn't that hard to learn to use and it's so useful, you should just consider this an invitation to give the process the old college try one more time.
Check the wrapper on your yarn. It will suggest how many stitches and how many rows you need for a gauge block.
I'm looking at a random label for Red Heart Supersaver worsted. It says 12SC along the bottom of the gauge square and 15R on the side. That's 12 single crochets across and 15 rows high. I'm in the US, so what I call a single crochet is what you, in the UK would call a double crochet. That's the first issue: make sure your yarn label, your pattern, and you are all using the same terminology.
Here's an article explaining the terms so you can translate between them: http://catherine-calder.wrytestuff.com/swa217600.htm
I want to make a swatch of 12 stitches. So I chain 12 sts, then I add 1 more chain for turning (no, I won't actually turn at this point, but it's still called a turning chain). Insert the hook into the second chain from the hook and make a stitch, then stitch the rest of the way across. I count as I go, to make sure I get 12 sts. If I accidentally chained too many at the beginning, I just ignore the extras and stop when I've got 12. It's just a gauge swatch, so it doesn't matter if it isn't perfect. Similarly, if I accidentally didn't allow enough, I could sneak two in one chain to make up the difference.
Now that I have 12 sts across, I'll do 14 more rows the same way. Then cut the yarn and tie off the end. Now I get out the ruler and measure my square through the center. It should be 10 cm each way. Gauge squares are always 10 cm unless they specifically say something else.
The most important measurement is the width of the piece. If I got 10 cm across, then I'm good and ready to start. If my square is less than 10 cm across, then I make a second square, this time using a larger hook and remeasure to see if I'm closer and if not, which direction (larger or smaller) I need to go next. If my square is more than 10 cm across, then I make another square using a smaller hook.
I think that for a lot of us who are used to doing gauge blocks/squares without thinking about it, it is easy to sort of skim over the details of how it is done. So I've described it in some greater detail in case it is a lack of clarity on some point that has made this process seem difficult when really it isn't. It's just a tad tedious when you'd rather get right on to the project. But it is a HUGE time and sanity saver if you catch a mistake in gauge before you've gone so far in the project that finding it just makes you want to cry.