The race for World Cup places gathers pace this weekend when England arrive in Cardiff for Wales' penultimate Test match ahead of their departure to New Zealand.
Wales coach Warren Gatland will name his 30-man squad in just under a fortnight's time, and Henson accepts the clock is ticking.
Jamie Roberts and Jonathan Davies appear to be installed as Gatland's premier midfield pairing, while Scarlets youngster Scott Williams has impressed greatly in training and when he featured as a replacement at Twickenham three days ago.
Henson is expected to be handed a chance at the Millennium Stadium on Saturday in what would be only his second Wales appearance since March 2009.
And having never played in a World Cup - he was overlooked eight years ago, and then ruled out by injury ahead of the 2007 tournament in France - the 29-year-old former Ospreys, Saracens and Toulon centre knows what is at stake.
After the return fixture against England, Wales host Argentina on August 20 before Gatland unveils his Wellington-bound party just 48 hours later.
"There is huge competition for places, and I just hope I get a chance in one of these games," said Henson.
"There are definitely three centres there at the moment, so I need to do something pretty special if I get the chance.
"It is about taking your chance and trying to get involved in this World Cup. I've never been to one, so it's huge for me.
"It would probably be one of the biggest achievements of my rugby career if I manage to do it. I missed out on the last two, and that still hurts."
Henson played a full part during Wales' punishing training camps at the Olympic sports village in Spala, Poland last month and there are no issues whatsoever with his fitness, despite minimal game time this year.
After numerous injury setbacks that prompted a long self-imposed exile from rugby which only ended last Christmas, the double Six Nations Grand Slam winner is ready to state his World Cup case.
"I've had quite a bit of time out - I haven't managed to have too many games under my belt - but the body is feeling good," added Henson, who started Wales' defeat to the Barbarians in early June.
"I really have missed it, being involved with Wales. It has been awesome, the fitness training has been tough but we have all got through it and I hope it pays dividends. I am raring to go.
"All the other centres are on top of their game. I will be feeling a bit of pressure in that this is (possibly) my last chance to make an impact to try to force my way into the World Cup squad.
"At the moment, I think the other three centres are probably ahead of me, which is fair enough. I will have to try to turn the tables and try to show something a bit different from what those three can offer."
Henson has also underlined his desire to play regional rugby in Wales again following stints in the Aviva Premiership and French Top 14.
"I have always said I hope the Ospreys would have me back," said Henson, who is currently without a club.
"I haven't spoken to them yet, but they will be the first people I will speak to.
"I just want to concentrate on Wales at the moment and try to get in that World Cup squad."
Stricken Wales and Scarlets back Morgan Stoddart, meanwhile, was due to arrive home from London's Charing Cross Hospital on Tuesday after undergoing successful surgery on his broken left leg.
Stoddart suffered the World Cup-ending injury during Wales' 23-19 defeat against England at Twickenham, and he will now prepare to start rehabilitation work with the Scarlets.
Scarlets head coach Nigel Davies said: "We are all really disappointed for Morgan.
"He has been on great form and quite obviously relishing his opportunities with Wales and the prospect of the World Cup, so it's a cruel blow.
"But he is doing well and is comfortable after the operation.
"He also knows he will have all the support he can get from the whole Scarlets team to get him back to fitness and healthy again at the earliest opportunity."
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