Budget consciously wishing to fly as follows:

21 Sept London-Amsterdam --- Easyjet. £30 sorted!
24 Sept Amsterdam-Helsinki
26 Sept Helsinki-London --- Easyjet. £43 sorted!


However, Ams-Hel return fare is £203 but the single is £450! Yikes!
(KLM or Finnair same price)

So, what happens if I buy the return ticket at £203, then? Can I just use the outward half and simply not check in or turn up for the return half?

Sorry if this is an ignorant question but I am a newbie novice!