Matching New Chainring to Freewheel

[Eugbug]

The chain is slipping on my MTB when I'm on the middle chainring and smallest sprocket on the back, but only when I put a lot of force on the pedals.  I replaced the chain last year along with the 7 speed freewheel and the middle 32T chainring. I've probably cycled only 1000 to 1500 miles since and tried to only oil the chain when it was clean, so I'm not sure whether it is excessively worn (have to check).
Should I just replace the chain? The smallest sprocket at the back doesn't look worn (no shark/hooked  teeth), so I don't think the chain is slipping on that, rather the chainring. If I buy a new chairing, does it need to be matched to the freewheel? Specs on ads mention that a chainring is for an e.g. 9 speed.

[Eugbug]

Checked chain over 12 inch span. There is a 1/4 inch stretch, so it's quite worn. It hasn't had a huge amount of mileage though, probably not more than 1500 miles.