Its usual to sow peas direct into the ground in a drill wide enough to plant three deep a few inches apart, in a sort of zig zag pattern. For early sowing some people have tried sowing into guttering pipe, and then sliding the whole lot into the ground. You will need to harden them off for a few days at least before you plant them out, unless you can give them some protection eg a plastic cloche run. They don't need wide spacing, a few inches will do.Doesn't it give you instructions on the packet? It sounds as though you have only sown a few, so if you have some seed left try sowing some more into the veg bed. Don't forget to give them some support.

Later... Just noticed from Moon Grower's blog that she sows them in newspaper pots in the greenhouse.

They will need to be hardened off first. I sow my first lot in guttering, Then the rest of the sowings are done direct. I follow the advice of a retired head Gardener, who told me to sow peas thicker than recommended on the packs, I create a drill 4" wide and 9' long and I use the whole packet that says sufficient for a 12' row. I have never had a problem with the numbers. and depending on Variety they can be self supporting. Kelvedon wonder is brill for this method.

Thank you both so much! I will start to harden them off now - I have 12 plants, all looking healthy, and there is only me so will I need to plant more? This is my first year with a small back garden so I am trying not to overwhelm myself with too many plants/gluts but it's so hard not to keep sowing and growing! Addicted already. I am planning to mix the veg in with other plants and won't really have straight lines but it is really helpful to know I can plant them a few inches apart. Thanks again, I really appreciate the help!

It would be better to grow a few more. If you love peas like we do. You could either sow them direct or as you have been. If you have space for a full row, sow some this week and some more in another couple of weeks and so on, That way you will have a continual supply.
If it is just borders in the garden, you could sow little blocks of them. Say about 40 in 2' sq. If it space you are stuck for, try Alderman, they are climbing peas to about 6'. And could go at the back of the border up a wigwam or fence.

Thank you very much 2ndhand! My peas are hardening off now, and I will try planting some direct as well as you suggest. I've got raised beds along 3 sides of a small back garden plus a raised bed in the middle specifically for veg. It's my first time growing anything so I'm learning as I go! Thanks again for taking the time to share your experience :)