I bought the same antenna for my t deck plus! Pretty happy with it.

I agree with the other poster, the Plus model comes with a small whip antenna, both of mine came with the same one. They likely sent you the wrong model.

If you don't want to hassle with a return (understandable given the time shipping takes for these) you can crak that bad boy open and attach a ufl to female sma pigtail like this https://www.waveform.com/products/sma-female-to-u-fl-pigtail-adapter-v2?srsltid=AfmBOorizL-HpE3bSg8TVlHToLh4av4USvaYiEYVKjVFdBmFUdMtTqbd but to be on the safe side do a search for sma types, there's several img references that will help. You really just need to make sure your antenna does or doesn't have the inside pin and buy the appropriate corresponding sma connector with a ufl pigtail on the other end.

I bought 2, with 5dbi antennas included, off Amazon a while back bc I wanted to add an external gps antenna to my first one. Word of warning if the case still has the little punchouts for external antenna, they are hard to cut out and make rounded enough for the sma to slip through.

I used model nippers and a round sanding stick to get the sma through that hole and it still ended to cracking the small ring of plastic on the case. It doesn't affect performance at all and the sma connector is solidly in place, but it can happen.